diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 28428f4f31fcb..6855002c129c4 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -635,6 +635,7 @@ namespace ts {
             isTupleType,
             isArrayLikeType,
             isTypeInvalidDueToUnionDiscriminant,
+            getExactOptionalProperties,
             getAllPossiblePropertiesOfTypes,
             getSuggestedSymbolForNonexistentProperty,
             getSuggestionForNonexistentProperty,
@@ -16768,24 +16769,29 @@ namespace ts {
                 let sourcePropType = getIndexedAccessTypeOrUndefined(source, nameType);
                 if (!sourcePropType) continue;
                 const propName = getPropertyNameFromIndex(nameType, /*accessNode*/ undefined);
-                const targetIsOptional = !!(propName && (getPropertyOfType(target, propName) || unknownSymbol).flags & SymbolFlags.Optional);
-                const sourceIsOptional = !!(propName && (getPropertyOfType(source, propName) || unknownSymbol).flags & SymbolFlags.Optional);
-                targetPropType = removeMissingType(targetPropType, targetIsOptional);
-                sourcePropType = removeMissingType(sourcePropType, targetIsOptional && sourceIsOptional);
                 if (!checkTypeRelatedTo(sourcePropType, targetPropType, relation, /*errorNode*/ undefined)) {
                     const elaborated = next && elaborateError(next, sourcePropType, targetPropType, relation, /*headMessage*/ undefined, containingMessageChain, errorOutputContainer);
-                    if (elaborated) {
-                        reportedError = true;
-                    }
-                    else {
+                    reportedError = true;
+                    if (!elaborated) {
                         // Issue error on the prop itself, since the prop couldn't elaborate the error
                         const resultObj: { errors?: Diagnostic[] } = errorOutputContainer || {};
                         // Use the expression type, if available
                         const specificSource = next ? checkExpressionForMutableLocationWithContextualType(next, sourcePropType) : sourcePropType;
-                        const result = checkTypeRelatedTo(specificSource, targetPropType, relation, prop, errorMessage, containingMessageChain, resultObj);
-                        if (result && specificSource !== sourcePropType) {
-                            // If for whatever reason the expression type doesn't yield an error, make sure we still issue an error on the sourcePropType
-                            checkTypeRelatedTo(sourcePropType, targetPropType, relation, prop, errorMessage, containingMessageChain, resultObj);
+                        if (exactOptionalPropertyTypes && isExactOptionalPropertyMismatch(specificSource, targetPropType)) {
+                            const diag = createDiagnosticForNode(prop, Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_type_of_the_target, typeToString(specificSource), typeToString(targetPropType));
+                            diagnostics.add(diag);
+                            resultObj.errors = [diag];
+                        }
+                        else {
+                            const targetIsOptional = !!(propName && (getPropertyOfType(target, propName) || unknownSymbol).flags & SymbolFlags.Optional);
+                            const sourceIsOptional = !!(propName && (getPropertyOfType(source, propName) || unknownSymbol).flags & SymbolFlags.Optional);
+                            targetPropType = removeMissingType(targetPropType, targetIsOptional);
+                            sourcePropType = removeMissingType(sourcePropType, targetIsOptional && sourceIsOptional);
+                            const result = checkTypeRelatedTo(specificSource, targetPropType, relation, prop, errorMessage, containingMessageChain, resultObj);
+                            if (result && specificSource !== sourcePropType) {
+                                // If for whatever reason the expression type doesn't yield an error, make sure we still issue an error on the sourcePropType
+                                checkTypeRelatedTo(sourcePropType, targetPropType, relation, prop, errorMessage, containingMessageChain, resultObj);
+                            }
                         }
                         if (resultObj.errors) {
                             const reportedDiag = resultObj.errors[resultObj.errors.length - 1];
@@ -16813,7 +16819,6 @@ namespace ts {
                                 }
                             }
                         }
-                        reportedError = true;
                     }
                 }
             }
@@ -17679,10 +17684,18 @@ namespace ts {
                     else if (sourceType === targetType) {
                         message = Diagnostics.Type_0_is_not_assignable_to_type_1_Two_different_types_with_this_name_exist_but_they_are_unrelated;
                     }
+                    else if (exactOptionalPropertyTypes && getExactOptionalUnassignableProperties(source, target).length) {
+                        message = Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_types_of_the_target_s_properties;
+                    }
                     else {
                         message = Diagnostics.Type_0_is_not_assignable_to_type_1;
                     }
                 }
+                else if (message === Diagnostics.Argument_of_type_0_is_not_assignable_to_parameter_of_type_1
+                    && exactOptionalPropertyTypes
+                    && getExactOptionalUnassignableProperties(source, target).length) {
+                    message = Diagnostics.Argument_of_type_0_is_not_assignable_to_parameter_of_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_types_of_the_target_s_properties;
+                }
 
                 reportError(message, generalizedSourceType, targetType);
             }
@@ -19598,6 +19611,20 @@ namespace ts {
             return isUnitType(type) || !!(type.flags & TypeFlags.TemplateLiteral);
         }
 
+        function getExactOptionalUnassignableProperties(source: Type, target: Type) {
+            if (isTupleType(source) && isTupleType(target)) return emptyArray;
+            return getPropertiesOfType(target)
+                .filter(targetProp => isExactOptionalPropertyMismatch(getTypeOfPropertyOfType(source, targetProp.escapedName), getTypeOfSymbol(targetProp)));
+        }
+
+        function isExactOptionalPropertyMismatch(source: Type | undefined, target: Type | undefined) {
+            return !!source && !!target && maybeTypeOfKind(source, TypeFlags.Undefined) && !!containsMissingType(target);
+        }
+
+        function getExactOptionalProperties(type: Type) {
+            return getPropertiesOfType(type).filter(targetProp => containsMissingType(getTypeOfSymbol(targetProp)));
+        }
+
         function getBestMatchingType(source: Type, target: UnionOrIntersectionType, isRelatedTo = compareTypesAssignable) {
             return findMatchingDiscriminantType(source, target, isRelatedTo, /*skipPartial*/ true) ||
                 findMatchingTypeReferenceOrTypeAliasReference(source, target) ||
@@ -32479,8 +32506,16 @@ namespace ts {
                         Diagnostics.The_left_hand_side_of_an_assignment_expression_must_be_a_variable_or_a_property_access,
                         Diagnostics.The_left_hand_side_of_an_assignment_expression_may_not_be_an_optional_property_access)
                         && (!isIdentifier(left) || unescapeLeadingUnderscores(left.escapedText) !== "exports")) {
+
+                        let headMessage: DiagnosticMessage | undefined;
+                        if (exactOptionalPropertyTypes && isPropertyAccessExpression(left) && maybeTypeOfKind(valueType, TypeFlags.Undefined)) {
+                            const target = getTypeOfPropertyOfType(getTypeOfExpression(left.expression), left.name.escapedText);
+                            if (isExactOptionalPropertyMismatch(valueType, target)) {
+                                headMessage = Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_type_of_the_target;
+                            }
+                        }
                         // to avoid cascading errors check assignability only if 'isReference' check succeeded and no errors were reported
-                        checkTypeAssignableToAndOptionallyElaborate(valueType, leftType, left, right);
+                        checkTypeAssignableToAndOptionallyElaborate(valueType, leftType, left, right, headMessage);
                     }
                 }
             }
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 64b6c87d12c5c..91780f5309c8d 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1738,6 +1738,10 @@
         "category": "Error",
         "code": 2374
     },
+    "Type '{0}' is not assignable to type '{1}' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.": {
+        "category": "Error",
+        "code": 2375
+    },
     "A 'super' call must be the first statement in the constructor when a class contains initialized properties, parameter properties, or private identifiers.": {
         "category": "Error",
         "code": 2376
@@ -1750,6 +1754,10 @@
         "category": "Error",
         "code": 2378
     },
+    "Argument of type '{0}' is not assignable to parameter of type '{1}' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.": {
+        "category": "Error",
+        "code": 2379
+    },
     "The return type of a 'get' accessor must be assignable to its 'set' accessor type": {
         "category": "Error",
         "code": 2380
@@ -1874,6 +1882,10 @@
         "category": "Error",
         "code": 2410
     },
+    "Type '{0}' is not assignable to type '{1}' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.": {
+        "category": "Error",
+        "code": 2412
+    },
     "Property '{0}' of type '{1}' is not assignable to '{2}' index type '{3}'.": {
         "category": "Error",
         "code": 2411
@@ -7118,6 +7130,10 @@
         "category": "Message",
         "code": 95168
     },
+    "Add 'undefined' to optional property type": {
+        "category": "Message",
+        "code": 95169
+    },
 
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer.": {
         "category": "Error",
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 4d13e803fb9b4..6194f41a20d22 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -4308,6 +4308,7 @@ namespace ts {
          * e.g. it specifies `kind: "a"` and obj has `kind: "b"`.
          */
         /* @internal */ isTypeInvalidDueToUnionDiscriminant(contextualType: Type, obj: ObjectLiteralExpression | JsxAttributes): boolean;
+        /* @internal */ getExactOptionalProperties(type: Type): Symbol[];
         /**
          * For a union, will include a property if it's defined in *any* of the member types.
          * So for `{ a } | { b }`, this will include both `a` and `b`.
diff --git a/src/harness/fourslashImpl.ts b/src/harness/fourslashImpl.ts
index af75c48f0bae0..322b00a81cfb7 100644
--- a/src/harness/fourslashImpl.ts
+++ b/src/harness/fourslashImpl.ts
@@ -641,7 +641,8 @@ namespace FourSlash {
                 if (errors.length) {
                     this.printErrorLog(/*expectErrors*/ false, errors);
                     const error = errors[0];
-                    this.raiseError(`Found an error: ${this.formatPosition(error.file!, error.start!)}: ${error.messageText}`);
+                    const message = typeof error.messageText === "string" ? error.messageText : error.messageText.messageText;
+                    this.raiseError(`Found an error: ${this.formatPosition(error.file!, error.start!)}: ${message}`);
                 }
             });
         }
diff --git a/src/services/codefixes/addMissingAwait.ts b/src/services/codefixes/addMissingAwait.ts
index e3a15d8864144..01f7ece1a0388 100644
--- a/src/services/codefixes/addMissingAwait.ts
+++ b/src/services/codefixes/addMissingAwait.ts
@@ -32,7 +32,7 @@ namespace ts.codefix {
         errorCodes,
         getCodeActions: context => {
             const { sourceFile, errorCode, span, cancellationToken, program } = context;
-            const expression = getFixableErrorSpanExpression(sourceFile, errorCode, span, cancellationToken, program);
+            const expression = getAwaitErrorSpanExpression(sourceFile, errorCode, span, cancellationToken, program);
             if (!expression) {
                 return;
             }
@@ -48,7 +48,7 @@ namespace ts.codefix {
             const checker = context.program.getTypeChecker();
             const fixedDeclarations = new Set<number>();
             return codeFixAll(context, errorCodes, (t, diagnostic) => {
-                const expression = getFixableErrorSpanExpression(sourceFile, diagnostic.code, diagnostic, cancellationToken, program);
+                const expression = getAwaitErrorSpanExpression(sourceFile, diagnostic.code, diagnostic, cancellationToken, program);
                 if (!expression) {
                     return;
                 }
@@ -59,6 +59,13 @@ namespace ts.codefix {
         },
     });
 
+    function getAwaitErrorSpanExpression(sourceFile: SourceFile, errorCode: number, span: TextSpan, cancellationToken: CancellationToken, program: Program) {
+        const expression = getFixableErrorSpanExpression(sourceFile, span);
+        return expression
+            && isMissingAwaitError(sourceFile, errorCode, span, cancellationToken, program)
+            && isInsideAwaitableBody(expression) ? expression : undefined;
+    }
+
     function getDeclarationSiteFix(context: CodeFixContext | CodeFixAllContext, expression: Expression, errorCode: number, checker: TypeChecker, trackChanges: ContextualTrackChangesFunction, fixedDeclarations?: Set<number>) {
         const { sourceFile, program, cancellationToken } = context;
         const awaitableInitializers = findAwaitableInitializers(expression, sourceFile, cancellationToken, program, checker);
@@ -95,23 +102,6 @@ namespace ts.codefix {
             some(relatedInformation, related => related.code === Diagnostics.Did_you_forget_to_use_await.code));
     }
 
-    function getFixableErrorSpanExpression(sourceFile: SourceFile, errorCode: number, span: TextSpan, cancellationToken: CancellationToken, program: Program): Expression | undefined {
-        const token = getTokenAtPosition(sourceFile, span.start);
-        // Checker has already done work to determine that await might be possible, and has attached
-        // related info to the node, so start by finding the expression that exactly matches up
-        // with the diagnostic range.
-        const expression = findAncestor(token, node => {
-            if (node.getStart(sourceFile) < span.start || node.getEnd() > textSpanEnd(span)) {
-                return "quit";
-            }
-            return isExpression(node) && textSpansEqual(span, createTextSpanFromNode(node, sourceFile));
-        }) as Expression | undefined;
-
-        return expression
-            && isMissingAwaitError(sourceFile, errorCode, span, cancellationToken, program)
-            && isInsideAwaitableBody(expression) ? expression : undefined;
-    }
-
     interface AwaitableInitializer {
         expression: Expression;
         declarationSymbol: Symbol;
diff --git a/src/services/codefixes/addOptionalPropertyUndefined.ts b/src/services/codefixes/addOptionalPropertyUndefined.ts
new file mode 100644
index 0000000000000..13b80ed8a11e1
--- /dev/null
+++ b/src/services/codefixes/addOptionalPropertyUndefined.ts
@@ -0,0 +1,96 @@
+/* @internal */
+namespace ts.codefix {
+    const addOptionalPropertyUndefined = "addOptionalPropertyUndefined";
+
+    const errorCodes = [
+        Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_type_of_the_target.code,
+        Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_types_of_the_target_s_properties.code,
+        Diagnostics.Argument_of_type_0_is_not_assignable_to_parameter_of_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_types_of_the_target_s_properties.code,
+    ];
+
+    registerCodeFix({
+        errorCodes,
+        getCodeActions(context) {
+            const typeChecker = context.program.getTypeChecker();
+            const toAdd = getPropertiesToAdd(context.sourceFile, context.span, typeChecker);
+            if (!toAdd.length) {
+                return undefined;
+            }
+            const changes = textChanges.ChangeTracker.with(context, t => addUndefinedToOptionalProperty(t, toAdd));
+            return [createCodeFixActionWithoutFixAll(addOptionalPropertyUndefined, changes, Diagnostics.Add_undefined_to_optional_property_type)];
+        },
+        fixIds: [addOptionalPropertyUndefined],
+    });
+
+    function getPropertiesToAdd(file: SourceFile, span: TextSpan, checker: TypeChecker): Symbol[] {
+        const sourceTarget = getSourceTarget(getFixableErrorSpanExpression(file, span), checker);
+        if (!sourceTarget) {
+            return emptyArray;
+        }
+        const { source: sourceNode, target: targetNode } = sourceTarget;
+        const target = shouldUseParentTypeOfProperty(sourceNode, targetNode, checker)
+            ? checker.getTypeAtLocation(targetNode.expression)
+            : checker.getTypeAtLocation(targetNode);
+        if (target.symbol?.declarations?.some(d => getSourceFileOfNode(d).fileName.match(/\.d\.ts$/))) {
+            return emptyArray;
+        }
+        return checker.getExactOptionalProperties(target);
+    }
+
+    function shouldUseParentTypeOfProperty(sourceNode: Node, targetNode: Node, checker: TypeChecker): targetNode is PropertyAccessExpression {
+        return isPropertyAccessExpression(targetNode)
+            && !!checker.getExactOptionalProperties(checker.getTypeAtLocation(targetNode.expression)).length
+            && checker.getTypeAtLocation(sourceNode) === checker.getUndefinedType();
+    }
+
+    /**
+     * Find the source and target of the incorrect assignment.
+     * The call is recursive for property assignments.
+     */
+    function getSourceTarget(errorNode: Node | undefined, checker: TypeChecker): { source: Node, target: Node } | undefined {
+        if (!errorNode) {
+            return undefined;
+        }
+        else if (isBinaryExpression(errorNode.parent) && errorNode.parent.operatorToken.kind === SyntaxKind.EqualsToken) {
+            return { source: errorNode.parent.right, target: errorNode.parent.left };
+        }
+        else if (isVariableDeclaration(errorNode.parent) && errorNode.parent.initializer) {
+            return { source: errorNode.parent.initializer, target: errorNode.parent.name };
+        }
+        else if (isCallExpression(errorNode.parent)) {
+            const n = checker.getSymbolAtLocation(errorNode.parent.expression);
+            if (!n?.valueDeclaration || !isFunctionLikeKind(n.valueDeclaration.kind)) return undefined;
+            if (!isExpression(errorNode)) return undefined;
+            const i = errorNode.parent.arguments.indexOf(errorNode);
+            if (i === -1) return undefined;
+            const name = (n.valueDeclaration as any as SignatureDeclaration).parameters[i].name;
+            if (isIdentifier(name)) return { source: errorNode, target: name };
+        }
+        else if (isPropertyAssignment(errorNode.parent) && isIdentifier(errorNode.parent.name) ||
+            isShorthandPropertyAssignment(errorNode.parent)) {
+            const parentTarget = getSourceTarget(errorNode.parent.parent, checker);
+            if (!parentTarget) return undefined;
+            const prop = checker.getPropertyOfType(checker.getTypeAtLocation(parentTarget.target), (errorNode.parent.name as Identifier).text);
+            const declaration = prop?.declarations?.[0];
+            if (!declaration) return undefined;
+            return {
+                source: isPropertyAssignment(errorNode.parent) ? errorNode.parent.initializer : errorNode.parent.name,
+                target: declaration
+            };
+        }
+        return undefined;
+    }
+
+    function addUndefinedToOptionalProperty(changes: textChanges.ChangeTracker, toAdd: Symbol[]) {
+        for (const add of toAdd) {
+            const d = add.valueDeclaration;
+            if (d && (isPropertySignature(d) || isPropertyDeclaration(d)) && d.type) {
+                const t = factory.createUnionTypeNode([
+                    ...d.type.kind === SyntaxKind.UnionType ? (d.type as UnionTypeNode).types : [d.type],
+                    factory.createTypeReferenceNode("undefined")
+                ]);
+                changes.replaceNode(d.getSourceFile(), d.type, t);
+            }
+        }
+    }
+}
diff --git a/src/services/tsconfig.json b/src/services/tsconfig.json
index f1aa438fefb57..1e0934804edda 100644
--- a/src/services/tsconfig.json
+++ b/src/services/tsconfig.json
@@ -57,6 +57,7 @@
         "codefixes/addMissingDeclareProperty.ts",
         "codefixes/addMissingInvocationForDecorator.ts",
         "codefixes/addNameToNamelessParameter.ts",
+        "codefixes/addOptionalPropertyUndefined.ts",
         "codefixes/annotateWithTypeFromJSDoc.ts",
         "codefixes/convertFunctionToEs6Class.ts",
         "codefixes/convertToAsyncFunction.ts",
diff --git a/src/services/utilities.ts b/src/services/utilities.ts
index 3d503bff65912..2142286b8c67a 100644
--- a/src/services/utilities.ts
+++ b/src/services/utilities.ts
@@ -3085,6 +3085,22 @@ namespace ts {
         return createTextSpanFromBounds(startPosition, endPosition === undefined ? startPosition : endPosition);
     }
 
+    /* @internal */
+    export function getFixableErrorSpanExpression(sourceFile: SourceFile, span: TextSpan): Expression | undefined {
+        const token = getTokenAtPosition(sourceFile, span.start);
+        // Checker has already done work to determine that await might be possible, and has attached
+        // related info to the node, so start by finding the expression that exactly matches up
+        // with the diagnostic range.
+        const expression = findAncestor(token, node => {
+            if (node.getStart(sourceFile) < span.start || node.getEnd() > textSpanEnd(span)) {
+                return "quit";
+            }
+            return isExpression(node) && textSpansEqual(span, createTextSpanFromNode(node, sourceFile));
+        }) as Expression | undefined;
+
+        return expression;
+    }
+
     /**
      * If the provided value is an array, the mapping function is applied to each element; otherwise, the mapping function is applied
      * to the provided value itself.
diff --git a/tests/baselines/reference/strictOptionalProperties1.errors.txt b/tests/baselines/reference/strictOptionalProperties1.errors.txt
index d0401220ec0db..68c7da1f9e449 100644
--- a/tests/baselines/reference/strictOptionalProperties1.errors.txt
+++ b/tests/baselines/reference/strictOptionalProperties1.errors.txt
@@ -1,9 +1,9 @@
-tests/cases/compiler/strictOptionalProperties1.ts(6,5): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(12,5): error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(6,5): error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+tests/cases/compiler/strictOptionalProperties1.ts(12,5): error TS2412: Type 'string | undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
   Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(20,9): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(28,9): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(53,5): error TS2322: Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(20,9): error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+tests/cases/compiler/strictOptionalProperties1.ts(28,9): error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+tests/cases/compiler/strictOptionalProperties1.ts(53,5): error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
 tests/cases/compiler/strictOptionalProperties1.ts(60,5): error TS2322: Type 'undefined' is not assignable to type 'string'.
 tests/cases/compiler/strictOptionalProperties1.ts(64,5): error TS2322: Type '[number, string?, string?]' is not assignable to type '[number, string?]'.
   Target allows only 2 element(s) but source may have more.
@@ -11,24 +11,43 @@ tests/cases/compiler/strictOptionalProperties1.ts(73,5): error TS2322: Type '[nu
   Target allows only 3 element(s) but source may have more.
 tests/cases/compiler/strictOptionalProperties1.ts(74,5): error TS2322: Type '[never?, never?, true?]' is not assignable to type '[number, string?, boolean?]'.
   Source provides no match for required element at position 0 in target.
-tests/cases/compiler/strictOptionalProperties1.ts(75,14): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(99,34): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(105,45): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(106,55): error TS2322: Type 'undefined' is not assignable to type 'boolean'.
-tests/cases/compiler/strictOptionalProperties1.ts(107,45): error TS2322: Type 'undefined' is not assignable to type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(107,56): error TS2322: Type 'undefined' is not assignable to type 'boolean'.
-tests/cases/compiler/strictOptionalProperties1.ts(111,31): error TS2322: Type 'undefined' is not assignable to type 'number'.
+tests/cases/compiler/strictOptionalProperties1.ts(75,5): error TS2322: Type '[number, undefined, true]' is not assignable to type '[number, string?, boolean?]'.
+  Type at position 1 in source is not compatible with type at position 1 in target.
+    Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(99,7): error TS2375: Type '{ foo: undefined; bar: string; }' is not assignable to type 'InputProps' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'foo' are incompatible.
+    Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(105,7): error TS2322: Type '[number, undefined]' is not assignable to type '[number, string?, boolean?]'.
+  Type at position 1 in source is not compatible with type at position 1 in target.
+    Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(106,7): error TS2322: Type '[number, string, undefined]' is not assignable to type '[number, string?, boolean?]'.
+  Type at position 2 in source is not compatible with type at position 2 in target.
+    Type 'undefined' is not assignable to type 'boolean'.
+tests/cases/compiler/strictOptionalProperties1.ts(107,7): error TS2322: Type '[number, undefined, undefined]' is not assignable to type '[number, string?, boolean?]'.
+  Type at position 1 in source is not compatible with type at position 1 in target.
+    Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/strictOptionalProperties1.ts(111,7): error TS2375: Type '{ foo: undefined; }' is not assignable to type '{ foo?: number; }' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'foo' are incompatible.
+    Type 'undefined' is not assignable to type 'number'.
 tests/cases/compiler/strictOptionalProperties1.ts(119,5): error TS2411: Property 'bar' of type 'string | undefined' is not assignable to 'string' index type 'string'.
-tests/cases/compiler/strictOptionalProperties1.ts(192,1): error TS2322: Type '{ a: number; b: string | undefined; }' is not assignable to type '{ [x: string]: string | number; }'.
+tests/cases/compiler/strictOptionalProperties1.ts(190,15): error TS2451: Cannot redeclare block-scoped variable 'e'.
+tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type 'string | boolean | undefined' is not assignable to type 'string | number | undefined'.
+  Type 'false' is not assignable to type 'string | number | undefined'.
+tests/cases/compiler/strictOptionalProperties1.ts(194,1): error TS2412: Type 'string | boolean | undefined' is not assignable to type 'string | number' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+  Type 'undefined' is not assignable to type 'string | number'.
+tests/cases/compiler/strictOptionalProperties1.ts(195,1): error TS2375: Type '{ name: string; email: undefined; }' is not assignable to type 'U2' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+  Types of property 'email' are incompatible.
+    Type 'undefined' is not assignable to type 'string | number'.
+tests/cases/compiler/strictOptionalProperties1.ts(206,13): error TS2451: Cannot redeclare block-scoped variable 'e'.
+tests/cases/compiler/strictOptionalProperties1.ts(210,1): error TS2322: Type '{ a: number; b: string | undefined; }' is not assignable to type '{ [x: string]: string | number; }'.
   Property 'b' is incompatible with index signature.
     Type 'string | undefined' is not assignable to type 'string | number'.
       Type 'undefined' is not assignable to type 'string | number'.
-tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{ a: number; b?: string | undefined; }' is not assignable to type '{ [x: string]: string | number; }'.
-  Property 'b' is incompatible with index signature.
-    Type 'string | undefined' is not assignable to type 'string | number'.
+tests/cases/compiler/strictOptionalProperties1.ts(211,1): error TS2322: Type 'string | boolean | undefined' is not assignable to type '{ [x: string]: string | number; }'.
+  Type 'undefined' is not assignable to type '{ [x: string]: string | number; }'.
 
 
-==== tests/cases/compiler/strictOptionalProperties1.ts (19 errors) ====
+==== tests/cases/compiler/strictOptionalProperties1.ts (23 errors) ====
     function f1(obj: { a?: string, b?: string | undefined }) {
         let a = obj.a;  // string | undefined
         let b = obj.b;  // string | undefined
@@ -36,7 +55,7 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
         obj.b = 'hello';
         obj.a = undefined;  // Error
         ~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+!!! error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
         obj.b = undefined;
     }
     
@@ -44,8 +63,8 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
         obj = obj;
         obj.a = obj.a;  // Error
         ~~~~~
-!!! error TS2322: Type 'string | undefined' is not assignable to type 'string'.
-!!! error TS2322:   Type 'undefined' is not assignable to type 'string'.
+!!! error TS2412: Type 'string | undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+!!! error TS2412:   Type 'undefined' is not assignable to type 'string'.
         obj.b = obj.b;
         if ('a' in obj) {
             obj.a;
@@ -55,7 +74,7 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
             obj.a;
             obj.a = obj.a;  // Error
             ~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+!!! error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
         }
         if (obj.hasOwnProperty('a')) {
             obj.a;
@@ -65,7 +84,7 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
             obj.a;
             obj.a = obj.a;  // Error
             ~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+!!! error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
         }
         if ('b' in obj) {
             obj.b;
@@ -92,7 +111,7 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
         obj.b = 'hello';
         obj.a = undefined;  // Error
         ~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+!!! error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
         obj.b = undefined;
     }
     
@@ -126,8 +145,10 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
 !!! error TS2322: Type '[never?, never?, true?]' is not assignable to type '[number, string?, boolean?]'.
 !!! error TS2322:   Source provides no match for required element at position 0 in target.
         t = [42, undefined, true];  // Error
-                 ~~~~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+        ~
+!!! error TS2322: Type '[number, undefined, true]' is not assignable to type '[number, string?, boolean?]'.
+!!! error TS2322:   Type at position 1 in source is not compatible with type at position 1 in target.
+!!! error TS2322:     Type 'undefined' is not assignable to type 'string'.
     }
     
     function f6() {
@@ -152,32 +173,38 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
     
     const defaultProps: Pick<Props, 'foo'> = { foo: 'foo' };
     const inputProps: InputProps = { foo: undefined, bar: 'bar' };
-                                     ~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
-!!! related TS6500 tests/cases/compiler/strictOptionalProperties1.ts:94:5: The expected type comes from property 'foo' which is declared here on type 'InputProps'
+          ~~~~~~~~~~
+!!! error TS2375: Type '{ foo: undefined; bar: string; }' is not assignable to type 'InputProps' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'foo' are incompatible.
+!!! error TS2375:     Type 'undefined' is not assignable to type 'string'.
     const completeProps: Props = { ...defaultProps, ...inputProps };
     
     // Example from #13195
     
     const t1: [number, string?, boolean?] = [1];
     const t2: [number, string?, boolean?] = [1, undefined];
-                                                ~~~~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
+          ~~
+!!! error TS2322: Type '[number, undefined]' is not assignable to type '[number, string?, boolean?]'.
+!!! error TS2322:   Type at position 1 in source is not compatible with type at position 1 in target.
+!!! error TS2322:     Type 'undefined' is not assignable to type 'string'.
     const t3: [number, string?, boolean?] = [1, "string", undefined];
-                                                          ~~~~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'boolean'.
+          ~~
+!!! error TS2322: Type '[number, string, undefined]' is not assignable to type '[number, string?, boolean?]'.
+!!! error TS2322:   Type at position 2 in source is not compatible with type at position 2 in target.
+!!! error TS2322:     Type 'undefined' is not assignable to type 'boolean'.
     const t4: [number, string?, boolean?] = [1, undefined, undefined];
-                                                ~~~~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'string'.
-                                                           ~~~~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'boolean'.
+          ~~
+!!! error TS2322: Type '[number, undefined, undefined]' is not assignable to type '[number, string?, boolean?]'.
+!!! error TS2322:   Type at position 1 in source is not compatible with type at position 1 in target.
+!!! error TS2322:     Type 'undefined' is not assignable to type 'string'.
     
     // Example from #13195
     
     const x: { foo?: number } = { foo: undefined };
-                                  ~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'number'.
-!!! related TS6500 tests/cases/compiler/strictOptionalProperties1.ts:111:12: The expected type comes from property 'foo' which is declared here on type '{ foo?: number; }'
+          ~
+!!! error TS2375: Type '{ foo: undefined; }' is not assignable to type '{ foo?: number; }' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'foo' are incompatible.
+!!! error TS2375:     Type 'undefined' is not assignable to type 'number'.
     const y: { foo: number } = { foo: 123, ...x };
     
     // Index signatures and strict optional properties
@@ -250,6 +277,36 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
     
     declare function bb(input: number): void;
     
+    interface U1 {
+        name: string
+        email?: string | number | undefined
+    }
+    interface U2 {
+        name: string
+        email?: string | number
+    }
+    declare const e: string | boolean | undefined
+                  ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'e'.
+    declare const u1: U1
+    declare let u2: U2
+    u1.email = e // error, but only because boolean isn't in email's type
+    ~~~~~~~~
+!!! error TS2322: Type 'string | boolean | undefined' is not assignable to type 'string | number | undefined'.
+!!! error TS2322:   Type 'false' is not assignable to type 'string | number | undefined'.
+    u2.email = e // error, and suggest adding undefined
+    ~~~~~~~~
+!!! error TS2412: Type 'string | boolean | undefined' is not assignable to type 'string | number' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.
+!!! error TS2412:   Type 'undefined' is not assignable to type 'string | number'.
+    u2 = {
+    ~~
+!!! error TS2375: Type '{ name: string; email: undefined; }' is not assignable to type 'U2' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
+!!! error TS2375:   Types of property 'email' are incompatible.
+!!! error TS2375:     Type 'undefined' is not assignable to type 'string | number'.
+        name: 'hi',
+        email: undefined
+    }
+    
     // Repro from #44437
     
     declare var a: {[x: string]: number | string }
@@ -257,6 +314,8 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
     declare var c: {a: number, b?: string}
     declare var d: {a: number, b: string | undefined }
     declare var e: {a: number, b?: string | undefined }
+                ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'e'.
     
     a = b;
     a = c;
@@ -268,7 +327,6 @@ tests/cases/compiler/strictOptionalProperties1.ts(193,1): error TS2322: Type '{
 !!! error TS2322:       Type 'undefined' is not assignable to type 'string | number'.
     a = e;  // Error
     ~
-!!! error TS2322: Type '{ a: number; b?: string | undefined; }' is not assignable to type '{ [x: string]: string | number; }'.
-!!! error TS2322:   Property 'b' is incompatible with index signature.
-!!! error TS2322:     Type 'string | undefined' is not assignable to type 'string | number'.
+!!! error TS2322: Type 'string | boolean | undefined' is not assignable to type '{ [x: string]: string | number; }'.
+!!! error TS2322:   Type 'undefined' is not assignable to type '{ [x: string]: string | number; }'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/strictOptionalProperties1.js b/tests/baselines/reference/strictOptionalProperties1.js
index 0ae9f9087f883..ba3536e97f7f4 100644
--- a/tests/baselines/reference/strictOptionalProperties1.js
+++ b/tests/baselines/reference/strictOptionalProperties1.js
@@ -180,6 +180,24 @@ function aa(input: Bar): void {
 
 declare function bb(input: number): void;
 
+interface U1 {
+    name: string
+    email?: string | number | undefined
+}
+interface U2 {
+    name: string
+    email?: string | number
+}
+declare const e: string | boolean | undefined
+declare const u1: U1
+declare let u2: U2
+u1.email = e // error, but only because boolean isn't in email's type
+u2.email = e // error, and suggest adding undefined
+u2 = {
+    name: 'hi',
+    email: undefined
+}
+
 // Repro from #44437
 
 declare var a: {[x: string]: number | string }
@@ -322,6 +340,12 @@ function aa(input) {
     var notUndefinedVal = expectNotUndefined(input.bar);
     bb(notUndefinedVal);
 }
+u1.email = e; // error, but only because boolean isn't in email's type
+u2.email = e; // error, and suggest adding undefined
+u2 = {
+    name: 'hi',
+    email: undefined
+};
 a = b;
 a = c;
 a = d; // Error
@@ -399,6 +423,17 @@ interface Bar {
 }
 declare function aa(input: Bar): void;
 declare function bb(input: number): void;
+interface U1 {
+    name: string;
+    email?: string | number | undefined;
+}
+interface U2 {
+    name: string;
+    email?: string | number;
+}
+declare const e: string | boolean | undefined;
+declare const u1: U1;
+declare let u2: U2;
 declare var a: {
     [x: string]: number | string;
 };
diff --git a/tests/baselines/reference/strictOptionalProperties1.symbols b/tests/baselines/reference/strictOptionalProperties1.symbols
index bb363740008ff..2cdd1ddce6dc0 100644
--- a/tests/baselines/reference/strictOptionalProperties1.symbols
+++ b/tests/baselines/reference/strictOptionalProperties1.symbols
@@ -571,45 +571,97 @@ declare function bb(input: number): void;
 >bb : Symbol(bb, Decl(strictOptionalProperties1.ts, 177, 1))
 >input : Symbol(input, Decl(strictOptionalProperties1.ts, 179, 20))
 
+interface U1 {
+>U1 : Symbol(U1, Decl(strictOptionalProperties1.ts, 179, 41))
+
+    name: string
+>name : Symbol(U1.name, Decl(strictOptionalProperties1.ts, 181, 14))
+
+    email?: string | number | undefined
+>email : Symbol(U1.email, Decl(strictOptionalProperties1.ts, 182, 16))
+}
+interface U2 {
+>U2 : Symbol(U2, Decl(strictOptionalProperties1.ts, 184, 1))
+
+    name: string
+>name : Symbol(U2.name, Decl(strictOptionalProperties1.ts, 185, 14))
+
+    email?: string | number
+>email : Symbol(U2.email, Decl(strictOptionalProperties1.ts, 186, 16))
+}
+declare const e: string | boolean | undefined
+>e : Symbol(e, Decl(strictOptionalProperties1.ts, 189, 13))
+
+declare const u1: U1
+>u1 : Symbol(u1, Decl(strictOptionalProperties1.ts, 190, 13))
+>U1 : Symbol(U1, Decl(strictOptionalProperties1.ts, 179, 41))
+
+declare let u2: U2
+>u2 : Symbol(u2, Decl(strictOptionalProperties1.ts, 191, 11))
+>U2 : Symbol(U2, Decl(strictOptionalProperties1.ts, 184, 1))
+
+u1.email = e // error, but only because boolean isn't in email's type
+>u1.email : Symbol(U1.email, Decl(strictOptionalProperties1.ts, 182, 16))
+>u1 : Symbol(u1, Decl(strictOptionalProperties1.ts, 190, 13))
+>email : Symbol(U1.email, Decl(strictOptionalProperties1.ts, 182, 16))
+>e : Symbol(e, Decl(strictOptionalProperties1.ts, 189, 13))
+
+u2.email = e // error, and suggest adding undefined
+>u2.email : Symbol(U2.email, Decl(strictOptionalProperties1.ts, 186, 16))
+>u2 : Symbol(u2, Decl(strictOptionalProperties1.ts, 191, 11))
+>email : Symbol(U2.email, Decl(strictOptionalProperties1.ts, 186, 16))
+>e : Symbol(e, Decl(strictOptionalProperties1.ts, 189, 13))
+
+u2 = {
+>u2 : Symbol(u2, Decl(strictOptionalProperties1.ts, 191, 11))
+
+    name: 'hi',
+>name : Symbol(name, Decl(strictOptionalProperties1.ts, 194, 6))
+
+    email: undefined
+>email : Symbol(email, Decl(strictOptionalProperties1.ts, 195, 15))
+>undefined : Symbol(undefined)
+}
+
 // Repro from #44437
 
 declare var a: {[x: string]: number | string }
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 183, 11))
->x : Symbol(x, Decl(strictOptionalProperties1.ts, 183, 17))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 201, 11))
+>x : Symbol(x, Decl(strictOptionalProperties1.ts, 201, 17))
 
 declare var b: {a: number, b: string}
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 184, 11))
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 184, 16))
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 184, 26))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 202, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 202, 16))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 202, 26))
 
 declare var c: {a: number, b?: string}
->c : Symbol(c, Decl(strictOptionalProperties1.ts, 185, 11))
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 185, 16))
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 185, 26))
+>c : Symbol(c, Decl(strictOptionalProperties1.ts, 203, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 203, 16))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 203, 26))
 
 declare var d: {a: number, b: string | undefined }
->d : Symbol(d, Decl(strictOptionalProperties1.ts, 186, 11))
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 186, 16))
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 186, 26))
+>d : Symbol(d, Decl(strictOptionalProperties1.ts, 204, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 204, 16))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 204, 26))
 
 declare var e: {a: number, b?: string | undefined }
->e : Symbol(e, Decl(strictOptionalProperties1.ts, 187, 11))
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 187, 16))
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 187, 26))
+>e : Symbol(e, Decl(strictOptionalProperties1.ts, 205, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 205, 16))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 205, 26))
 
 a = b;
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 183, 11))
->b : Symbol(b, Decl(strictOptionalProperties1.ts, 184, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 201, 11))
+>b : Symbol(b, Decl(strictOptionalProperties1.ts, 202, 11))
 
 a = c;
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 183, 11))
->c : Symbol(c, Decl(strictOptionalProperties1.ts, 185, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 201, 11))
+>c : Symbol(c, Decl(strictOptionalProperties1.ts, 203, 11))
 
 a = d;  // Error
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 183, 11))
->d : Symbol(d, Decl(strictOptionalProperties1.ts, 186, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 201, 11))
+>d : Symbol(d, Decl(strictOptionalProperties1.ts, 204, 11))
 
 a = e;  // Error
->a : Symbol(a, Decl(strictOptionalProperties1.ts, 183, 11))
->e : Symbol(e, Decl(strictOptionalProperties1.ts, 187, 11))
+>a : Symbol(a, Decl(strictOptionalProperties1.ts, 201, 11))
+>e : Symbol(e, Decl(strictOptionalProperties1.ts, 189, 13))
 
diff --git a/tests/baselines/reference/strictOptionalProperties1.types b/tests/baselines/reference/strictOptionalProperties1.types
index 939bb5d724390..4eb23fd31c8d0 100644
--- a/tests/baselines/reference/strictOptionalProperties1.types
+++ b/tests/baselines/reference/strictOptionalProperties1.types
@@ -683,6 +683,57 @@ declare function bb(input: number): void;
 >bb : (input: number) => void
 >input : number
 
+interface U1 {
+    name: string
+>name : string
+
+    email?: string | number | undefined
+>email : string | number | undefined
+}
+interface U2 {
+    name: string
+>name : string
+
+    email?: string | number
+>email : string | number | undefined
+}
+declare const e: string | boolean | undefined
+>e : string | boolean | undefined
+
+declare const u1: U1
+>u1 : U1
+
+declare let u2: U2
+>u2 : U2
+
+u1.email = e // error, but only because boolean isn't in email's type
+>u1.email = e : string | boolean | undefined
+>u1.email : string | number | undefined
+>u1 : U1
+>email : string | number | undefined
+>e : string | boolean | undefined
+
+u2.email = e // error, and suggest adding undefined
+>u2.email = e : string | boolean | undefined
+>u2.email : string | number
+>u2 : U2
+>email : string | number
+>e : string | boolean | undefined
+
+u2 = {
+>u2 = {    name: 'hi',    email: undefined} : { name: string; email: undefined; }
+>u2 : U2
+>{    name: 'hi',    email: undefined} : { name: string; email: undefined; }
+
+    name: 'hi',
+>name : string
+>'hi' : "hi"
+
+    email: undefined
+>email : undefined
+>undefined : undefined
+}
+
 // Repro from #44437
 
 declare var a: {[x: string]: number | string }
@@ -725,7 +776,7 @@ a = d;  // Error
 >d : { a: number; b: string | undefined; }
 
 a = e;  // Error
->a = e : { a: number; b?: string | undefined; }
+>a = e : string | boolean | undefined
 >a : { [x: string]: string | number; }
->e : { a: number; b?: string | undefined; }
+>e : string | boolean | undefined
 
diff --git a/tests/cases/compiler/strictOptionalProperties1.ts b/tests/cases/compiler/strictOptionalProperties1.ts
index 323dfa7eac976..2babf2bdb5bf1 100644
--- a/tests/cases/compiler/strictOptionalProperties1.ts
+++ b/tests/cases/compiler/strictOptionalProperties1.ts
@@ -183,6 +183,24 @@ function aa(input: Bar): void {
 
 declare function bb(input: number): void;
 
+interface U1 {
+    name: string
+    email?: string | number | undefined
+}
+interface U2 {
+    name: string
+    email?: string | number
+}
+declare const e: string | boolean | undefined
+declare const u1: U1
+declare let u2: U2
+u1.email = e // error, but only because boolean isn't in email's type
+u2.email = e // error, and suggest adding undefined
+u2 = {
+    name: 'hi',
+    email: undefined
+}
+
 // Repro from #44437
 
 declare var a: {[x: string]: number | string }
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties1.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties1.ts
new file mode 100644
index 0000000000000..993263eeb003e
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties1.ts
@@ -0,0 +1,32 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface I {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var i: I
+//// declare var j: J
+//// i/**/ = j
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface I {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var i: I
+declare var j: J
+i = j`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties10.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties10.ts
new file mode 100644
index 0000000000000..57065123f1636
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties10.ts
@@ -0,0 +1,32 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface IF {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// function fi(if_: IF) { return if_ }
+//// fi(j/**/)
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface IF {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+function fi(if_: IF) { return if_ }
+fi(j)`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties11.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties11.ts
new file mode 100644
index 0000000000000..094c0288ecead
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties11.ts
@@ -0,0 +1,36 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface IC {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// class C {
+////     ic: IC
+////     m() { this.ic/**/ = j }
+//// }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface IC {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+class C {
+    ic: IC
+    m() { this.ic = j }
+}`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties12.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties12.ts
new file mode 100644
index 0000000000000..0e81cc8e67e11
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties12.ts
@@ -0,0 +1,38 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface IC2 {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// class C {
+////     ic2: IC2
+//// }
+//// var c = new C()
+//// c.ic2/**/ = j
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface IC2 {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+class C {
+    ic2: IC2
+}
+var c = new C()
+c.ic2 = j`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties13.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties13.ts
new file mode 100644
index 0000000000000..f2209299ff08d
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties13.ts
@@ -0,0 +1,36 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface ICP {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// class CP {
+////     #icp: ICP
+////     m() { this.#icp/**/ = j; console.log(this.#icp) }
+//// }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface ICP {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+class CP {
+    #icp: ICP
+    m() { this.#icp = j; console.log(this.#icp) }
+}`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties14.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties14.ts
new file mode 100644
index 0000000000000..73d45770cb30e
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties14.ts
@@ -0,0 +1,32 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface ID {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// declare var id: ID
+//// ({ id/**/ } = { id: j })
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface ID {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+declare var id: ID
+({ id } = { id: j })`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties15.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties15.ts
new file mode 100644
index 0000000000000..ada582dfcf9fd
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties15.ts
@@ -0,0 +1,34 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface More {
+////     a?: number
+////     b?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// declare var more: More
+//// more/**/ = j
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface More {
+    a?: number | undefined
+    b?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+declare var more: More
+more = j`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties16.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties16.ts
new file mode 100644
index 0000000000000..4ab2c6549fb3a
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties16.ts
@@ -0,0 +1,30 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface Assignment {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// var assignment/**/: Assignment = j
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface Assignment {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+var assignment: Assignment = j`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties17.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties17.ts
new file mode 100644
index 0000000000000..7d45bff83ffef
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties17.ts
@@ -0,0 +1,30 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface PropertyAssignment {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// var opa/**/: { pa: PropertyAssignment } = { pa: j }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface PropertyAssignment {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+var opa: { pa: PropertyAssignment } = { pa: j }`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties18.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties18.ts
new file mode 100644
index 0000000000000..fe7f9f87b5b0b
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties18.ts
@@ -0,0 +1,30 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface ShorthandPropertyAssignment {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// var ospa/**/: { j: ShorthandPropertyAssignment } = { j }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface ShorthandPropertyAssignment {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+var ospa: { j: ShorthandPropertyAssignment } = { j }`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties19.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties19.ts
new file mode 100644
index 0000000000000..39771c61e2cf9
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties19.ts
@@ -0,0 +1,32 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface FPA {
+////     a?: number
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var j: J
+//// declare function fpa(fpa: { fpa: FPA }): void
+//// fpa({ fpa: j }/**/)
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface FPA {
+    a?: number | undefined
+}
+interface J {
+    a?: number | undefined
+}
+declare var j: J
+declare function fpa(fpa: { fpa: FPA }): void
+fpa({ fpa: j })`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties3.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties3.ts
new file mode 100644
index 0000000000000..12f508e4e9a82
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties3.ts
@@ -0,0 +1,18 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties2.ts
+//// import { INodeModules } from 'foo'
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var inm: INodeModules
+//// declare var j: J
+//// inm/**/ = j
+//// console.log(inm)
+// @Filename: node_modules/@types/foo/index.d.ts
+//// export interface INodeModules {
+////     a?: number
+//// }
+verify.codeFixAvailable([]);
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties4.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties4.ts
new file mode 100644
index 0000000000000..466bfdf7e3051
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties4.ts
@@ -0,0 +1,30 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties4.ts
+//// interface User {
+////     name: string
+////     email?: string
+//// }
+//// const user: User = {
+////     name: "Andrew",
+////     email: undefined,
+//// }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface User {
+    name: string
+    email?: string | undefined
+}
+const user: User = {
+    name: "Andrew",
+    email: undefined,
+}`,
+});
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties5.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties5.ts
new file mode 100644
index 0000000000000..8756c3002a5c0
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties5.ts
@@ -0,0 +1,27 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties5.ts
+//// interface User {
+////     name: string
+////     email?: string
+//// }
+//// declare const user: User
+//// user.email = undefined;
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`interface User {
+    name: string
+    email?: string | undefined
+}
+declare const user: User
+user.email = undefined;`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties6.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties6.ts
new file mode 100644
index 0000000000000..32eb41a370288
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties6.ts
@@ -0,0 +1,29 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties6.ts
+// based on snapshotterInjected.ts in microsoft/playwright
+//// type Data = {
+////     f?: (x: number) => void,
+////     additional?: number,
+////     nop: string,
+//// };
+//// declare function e(o: any): Data;
+//// e(101).f = undefined
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`type Data = {
+    f?: ((x: number) => void) | undefined,
+    additional?: number | undefined,
+    nop: string,
+};
+declare function e(o: any): Data;
+e(101).f = undefined`,
+});
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties7.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties7.ts
new file mode 100644
index 0000000000000..43b60f51d8989
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties7.ts
@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties6.ts
+// based on snapshotterInjected.ts in microsoft/playwright
+//// class Feh {
+////     _requestFinished(error?: string) {
+////         this._finishedPromiseCallback({ error/**/ });
+////     }
+////     private _finishedPromiseCallback: (arg: { error?: string }) => void = () => {};
+//// }
+verify.codeFixAvailable([ ]);
\ No newline at end of file
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties8.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties8.ts
new file mode 100644
index 0000000000000..b87ce681b203d
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties8.ts
@@ -0,0 +1,29 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+// @Filename: fixExactOptionalUnassignableProperties6.ts
+// based on snapshotterInjected.ts in microsoft/playwright
+//// type Data = {
+////     x?: {
+////         y?: number
+////     }
+//// }
+//// declare var d: Data
+//// d.x = { y: undefined }
+verify.codeFixAvailable([
+    { description: ts.Diagnostics.Add_undefined_to_optional_property_type.message }
+]);
+verify.codeFix({
+    description: ts.Diagnostics.Add_undefined_to_optional_property_type.message,
+    index: 0,
+    newFileContent:
+`type Data = {
+    x?: {
+        y?: number | undefined
+    }
+}
+declare var d: Data
+d.x = { y: undefined }`,
+});
+
diff --git a/tests/cases/fourslash/fixExactOptionalUnassignableProperties9.ts b/tests/cases/fourslash/fixExactOptionalUnassignableProperties9.ts
new file mode 100644
index 0000000000000..54ddf6c450417
--- /dev/null
+++ b/tests/cases/fourslash/fixExactOptionalUnassignableProperties9.ts
@@ -0,0 +1,14 @@
+/// <reference path='fourslash.ts'/>
+
+// @strictNullChecks: true
+// @exactOptionalPropertyTypes: true
+//// interface IAny {
+////     a?: any
+//// }
+//// interface J {
+////     a?: number | undefined
+//// }
+//// declare var iany: IAny
+//// declare var j: J
+//// iany/**/ = j
+verify.codeFixAvailable([]);