diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 4d4f1bf69a808..b89d2679ee619 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -19103,9 +19103,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [index]);
         const templateMapper = combineTypeMappers(objectType.mapper, mapper);
         const instantiatedTemplateType = instantiateType(getTemplateTypeFromMappedType(objectType.target as MappedType || objectType), templateMapper);
-        const isOptional = getMappedTypeOptionality(objectType) > 0 || (isGenericType(objectType) ?
-            getCombinedMappedTypeOptionality(getModifiersTypeFromMappedType(objectType)) > 0 :
-            couldAccessOptionalProperty(objectType, index));
+        const isOptional = isGenericType(objectType) ?
+            getCombinedMappedTypeOptionality(objectType) > 0 :
+            getMappedTypeOptionality(objectType) > 0 || couldAccessOptionalProperty(objectType, index);
         return addOptionality(instantiatedTemplateType, /*isProperty*/ true, isOptional);
     }
 
diff --git a/tests/baselines/reference/genericMappedTypeOptionalityModifier1.errors.txt b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.errors.txt
new file mode 100644
index 0000000000000..ae2828fffda00
--- /dev/null
+++ b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.errors.txt
@@ -0,0 +1,20 @@
+genericMappedTypeOptionalityModifier1.ts(10,9): error TS2322: Type 'undefined' is not assignable to type 'RequiredValues'.
+
+
+==== genericMappedTypeOptionalityModifier1.ts (1 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/59902
+    
+    const example = <T extends string>() => {
+      type SomeOptional = { [key in T]?: 1 };
+    
+      type AllRequired = { [key in keyof SomeOptional]-?: 1 };
+    
+      type RequiredValues = AllRequired[keyof AllRequired];
+    
+      const x: RequiredValues = undefined; // error
+            ~
+!!! error TS2322: Type 'undefined' is not assignable to type 'RequiredValues'.
+    
+      return x;
+    };
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/genericMappedTypeOptionalityModifier1.symbols b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.symbols
new file mode 100644
index 0000000000000..a85768348f070
--- /dev/null
+++ b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.symbols
@@ -0,0 +1,34 @@
+//// [tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts] ////
+
+=== genericMappedTypeOptionalityModifier1.ts ===
+// https://github.com/microsoft/TypeScript/issues/59902
+
+const example = <T extends string>() => {
+>example : Symbol(example, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 5))
+>T : Symbol(T, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 17))
+
+  type SomeOptional = { [key in T]?: 1 };
+>SomeOptional : Symbol(SomeOptional, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 41))
+>key : Symbol(key, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 25))
+>T : Symbol(T, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 17))
+
+  type AllRequired = { [key in keyof SomeOptional]-?: 1 };
+>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))
+>key : Symbol(key, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 24))
+>SomeOptional : Symbol(SomeOptional, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 41))
+
+  type RequiredValues = AllRequired[keyof AllRequired];
+>RequiredValues : Symbol(RequiredValues, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 58))
+>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))
+>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))
+
+  const x: RequiredValues = undefined; // error
+>x : Symbol(x, Decl(genericMappedTypeOptionalityModifier1.ts, 9, 7))
+>RequiredValues : Symbol(RequiredValues, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 58))
+>undefined : Symbol(undefined)
+
+  return x;
+>x : Symbol(x, Decl(genericMappedTypeOptionalityModifier1.ts, 9, 7))
+
+};
+
diff --git a/tests/baselines/reference/genericMappedTypeOptionalityModifier1.types b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.types
new file mode 100644
index 0000000000000..5fda3e59615a9
--- /dev/null
+++ b/tests/baselines/reference/genericMappedTypeOptionalityModifier1.types
@@ -0,0 +1,35 @@
+//// [tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts] ////
+
+=== genericMappedTypeOptionalityModifier1.ts ===
+// https://github.com/microsoft/TypeScript/issues/59902
+
+const example = <T extends string>() => {
+>example : <T extends string>() => { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
+>        : ^ ^^^^^^^^^      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+><T extends string>() => {  type SomeOptional = { [key in T]?: 1 };  type AllRequired = { [key in keyof SomeOptional]-?: 1 };  type RequiredValues = AllRequired[keyof AllRequired];  const x: RequiredValues = undefined; // error  return x;} : <T extends string>() => { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
+>                                                                                                                                                                                                                                               : ^ ^^^^^^^^^      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  type SomeOptional = { [key in T]?: 1 };
+>SomeOptional : { [key in T]?: 1 | undefined; }
+>             : ^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  type AllRequired = { [key in keyof SomeOptional]-?: 1 };
+>AllRequired : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }
+>            : ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  type RequiredValues = AllRequired[keyof AllRequired];
+>RequiredValues : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
+>               : ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  const x: RequiredValues = undefined; // error
+>x : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
+>  : ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>undefined : undefined
+>          : ^^^^^^^^^
+
+  return x;
+>x : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
+>  : ^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+};
+
diff --git a/tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts b/tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts
new file mode 100644
index 0000000000000..cba5520e4c5e4
--- /dev/null
+++ b/tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts
@@ -0,0 +1,16 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/59902
+
+const example = <T extends string>() => {
+  type SomeOptional = { [key in T]?: 1 };
+
+  type AllRequired = { [key in keyof SomeOptional]-?: 1 };
+
+  type RequiredValues = AllRequired[keyof AllRequired];
+
+  const x: RequiredValues = undefined; // error
+
+  return x;
+};