diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ce644034b9c3b..82d1ab321f2b9 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11896,6 +11896,9 @@ namespace ts {
                     else if ((type as MappedType).objectFlags & ObjectFlags.Mapped) {
                         resolveMappedTypeMembers(type as MappedType);
                     }
+                    else {
+                        Debug.fail("Unhandled object type " + Debug.formatObjectFlags(type.objectFlags));
+                    }
                 }
                 else if (type.flags & TypeFlags.Union) {
                     resolveUnionTypeMembers(type as UnionType);
@@ -11903,6 +11906,9 @@ namespace ts {
                 else if (type.flags & TypeFlags.Intersection) {
                     resolveIntersectionTypeMembers(type as IntersectionType);
                 }
+                else {
+                    Debug.fail("Unhandled type " + Debug.formatTypeFlags(type.flags));
+                }
             }
             return type as ResolvedType;
         }
@@ -24613,7 +24619,7 @@ namespace ts {
                 }
                 // for (const _ in ref) acts as a nonnull on ref
                 if (isVariableDeclaration(node) && node.parent.parent.kind === SyntaxKind.ForInStatement && isMatchingReference(reference, node.parent.parent.expression)) {
-                    return getNonNullableTypeIfNeeded(getTypeFromFlowType(getTypeAtFlowNode(flow.antecedent)));
+                    return getNonNullableTypeIfNeeded(finalizeEvolvingArrayType(getTypeFromFlowType(getTypeAtFlowNode(flow.antecedent))));
                 }
                 // Assignment doesn't affect reference
                 return undefined;
diff --git a/tests/baselines/reference/evolvingArrayResolvedAssert.errors.txt b/tests/baselines/reference/evolvingArrayResolvedAssert.errors.txt
new file mode 100644
index 0000000000000..487ffa3a82a12
--- /dev/null
+++ b/tests/baselines/reference/evolvingArrayResolvedAssert.errors.txt
@@ -0,0 +1,18 @@
+tests/cases/compiler/evolvingArrayResolvedAssert.ts(1,5): error TS7034: Variable 'C' implicitly has type 'any[]' in some locations where its type cannot be determined.
+tests/cases/compiler/evolvingArrayResolvedAssert.ts(2,15): error TS7005: Variable 'C' implicitly has an 'any[]' type.
+tests/cases/compiler/evolvingArrayResolvedAssert.ts(3,9): error TS7005: Variable 'C' implicitly has an 'any[]' type.
+
+
+==== tests/cases/compiler/evolvingArrayResolvedAssert.ts (3 errors) ====
+    var C = [];
+        ~
+!!! error TS7034: Variable 'C' implicitly has type 'any[]' in some locations where its type cannot be determined.
+    for (var a in C) {
+                  ~
+!!! error TS7005: Variable 'C' implicitly has an 'any[]' type.
+        if (C.hasOwnProperty(a)) {
+            ~
+!!! error TS7005: Variable 'C' implicitly has an 'any[]' type.
+        }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/evolvingArrayResolvedAssert.js b/tests/baselines/reference/evolvingArrayResolvedAssert.js
new file mode 100644
index 0000000000000..4cae93bbb8645
--- /dev/null
+++ b/tests/baselines/reference/evolvingArrayResolvedAssert.js
@@ -0,0 +1,15 @@
+//// [evolvingArrayResolvedAssert.ts]
+var C = [];
+for (var a in C) {
+    if (C.hasOwnProperty(a)) {
+    }
+}
+
+
+//// [evolvingArrayResolvedAssert.js]
+"use strict";
+var C = [];
+for (var a in C) {
+    if (C.hasOwnProperty(a)) {
+    }
+}
diff --git a/tests/baselines/reference/evolvingArrayResolvedAssert.symbols b/tests/baselines/reference/evolvingArrayResolvedAssert.symbols
new file mode 100644
index 0000000000000..8d52f9e5d0266
--- /dev/null
+++ b/tests/baselines/reference/evolvingArrayResolvedAssert.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/evolvingArrayResolvedAssert.ts ===
+var C = [];
+>C : Symbol(C, Decl(evolvingArrayResolvedAssert.ts, 0, 3))
+
+for (var a in C) {
+>a : Symbol(a, Decl(evolvingArrayResolvedAssert.ts, 1, 8))
+>C : Symbol(C, Decl(evolvingArrayResolvedAssert.ts, 0, 3))
+
+    if (C.hasOwnProperty(a)) {
+>C.hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
+>C : Symbol(C, Decl(evolvingArrayResolvedAssert.ts, 0, 3))
+>hasOwnProperty : Symbol(Object.hasOwnProperty, Decl(lib.es5.d.ts, --, --))
+>a : Symbol(a, Decl(evolvingArrayResolvedAssert.ts, 1, 8))
+    }
+}
+
diff --git a/tests/baselines/reference/evolvingArrayResolvedAssert.types b/tests/baselines/reference/evolvingArrayResolvedAssert.types
new file mode 100644
index 0000000000000..b0524c275c117
--- /dev/null
+++ b/tests/baselines/reference/evolvingArrayResolvedAssert.types
@@ -0,0 +1,18 @@
+=== tests/cases/compiler/evolvingArrayResolvedAssert.ts ===
+var C = [];
+>C : any[]
+>[] : never[]
+
+for (var a in C) {
+>a : string
+>C : any[]
+
+    if (C.hasOwnProperty(a)) {
+>C.hasOwnProperty(a) : boolean
+>C.hasOwnProperty : (v: PropertyKey) => boolean
+>C : any[]
+>hasOwnProperty : (v: PropertyKey) => boolean
+>a : string
+    }
+}
+
diff --git a/tests/cases/compiler/evolvingArrayResolvedAssert.ts b/tests/cases/compiler/evolvingArrayResolvedAssert.ts
new file mode 100644
index 0000000000000..7ba37947b0414
--- /dev/null
+++ b/tests/cases/compiler/evolvingArrayResolvedAssert.ts
@@ -0,0 +1,7 @@
+// @strict: true
+
+var C = [];
+for (var a in C) {
+    if (C.hasOwnProperty(a)) {
+    }
+}