diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 80b61edd3657a..11326c3ad83b8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1367,6 +1367,12 @@ const enum MappedTypeModifiers {
     ExcludeOptional = 1 << 3,
 }
 
+const enum MappedTypeModifierChange {
+    Stripped = -1,
+    Unchanged = 0,
+    Added = 1,
+}
+
 const enum MappedTypeNameTypeKind {
     None,
     Filtering,
@@ -14323,25 +14329,36 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             (declaration.questionToken ? declaration.questionToken.kind === SyntaxKind.MinusToken ? MappedTypeModifiers.ExcludeOptional : MappedTypeModifiers.IncludeOptional : 0);
     }
 
-    // Return -1, 0, or 1, where -1 means optionality is stripped (i.e. -?), 0 means optionality is unchanged, and 1 means
-    // optionality is added (i.e. +?).
-    function getMappedTypeOptionality(type: MappedType): number {
+    function getMappedTypeOptionality(type: MappedType): MappedTypeModifierChange {
+        const modifiers = getMappedTypeModifiers(type);
+        return modifiers & MappedTypeModifiers.ExcludeOptional ? MappedTypeModifierChange.Stripped : modifiers & MappedTypeModifiers.IncludeOptional ? MappedTypeModifierChange.Added : MappedTypeModifierChange.Unchanged;
+    }
+
+    function getMappedTypeReadonlyness(type: MappedType): MappedTypeModifierChange {
         const modifiers = getMappedTypeModifiers(type);
-        return modifiers & MappedTypeModifiers.ExcludeOptional ? -1 : modifiers & MappedTypeModifiers.IncludeOptional ? 1 : 0;
+        return modifiers & MappedTypeModifiers.ExcludeReadonly ? MappedTypeModifierChange.Stripped : modifiers & MappedTypeModifiers.IncludeReadonly ? MappedTypeModifierChange.Added : MappedTypeModifierChange.Unchanged;
     }
 
-    // Return -1, 0, or 1, for stripped, unchanged, or added optionality respectively. When a homomorphic mapped type doesn't
-    // modify optionality, recursively consult the optionality of the type being mapped over to see if it strips or adds optionality.
-    // For intersections, return -1 or 1 when all constituents strip or add optionality, otherwise return 0.
-    function getCombinedMappedTypeOptionality(type: Type): number {
+    // Return -1, 0, or 1, for stripped, unchanged, or added modifier kind respectively. When a homomorphic mapped type doesn't
+    // modify a modifier, recursively consult the modifier change of the type being mapped over to see if it strips or adds it.
+    // For intersections, return -1 or 1 when all constituents strip or add a specific modifier, otherwise return 0.
+    function getCombinedMappedTypeModifierChange(type: Type, getMappedTypeModifierChange: (type: MappedType) => MappedTypeModifierChange): MappedTypeModifierChange {
         if (getObjectFlags(type) & ObjectFlags.Mapped) {
-            return getMappedTypeOptionality(type as MappedType) || getCombinedMappedTypeOptionality(getModifiersTypeFromMappedType(type as MappedType));
+            return getMappedTypeModifierChange(type as MappedType) || getCombinedMappedTypeModifierChange(getModifiersTypeFromMappedType(type as MappedType), getMappedTypeModifierChange);
         }
         if (type.flags & TypeFlags.Intersection) {
-            const optionality = getCombinedMappedTypeOptionality((type as IntersectionType).types[0]);
-            return every((type as IntersectionType).types, (t, i) => i === 0 || getCombinedMappedTypeOptionality(t) === optionality) ? optionality : 0;
+            const modifierChange = getCombinedMappedTypeModifierChange((type as IntersectionType).types[0], getMappedTypeModifierChange);
+            return every((type as IntersectionType).types, (t, i) => i === 0 || getCombinedMappedTypeModifierChange(t, getMappedTypeModifierChange) === modifierChange) ? modifierChange : MappedTypeModifierChange.Unchanged;
         }
-        return 0;
+        return MappedTypeModifierChange.Unchanged;
+    }
+
+    function getCombinedMappedTypeOptionality(type: Type): MappedTypeModifierChange {
+        return getCombinedMappedTypeModifierChange(type, getMappedTypeOptionality);
+    }
+
+    function getCombinedMappedTypeReadonlyness(type: Type): MappedTypeModifierChange {
+        return getCombinedMappedTypeModifierChange(type, getMappedTypeReadonlyness);
     }
 
     function isPartialMappedType(type: Type) {
@@ -18244,6 +18261,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const nameType = getNameTypeFromMappedType(type.target as MappedType || type);
         if (!nameType && !(indexFlags & IndexFlags.NoIndexSignatures)) {
             // no mapping and no filtering required, just quickly bail to returning the constraint in the common case
+            // andarist
             return constraintType;
         }
         const keyTypes: Type[] = [];
@@ -18352,7 +18370,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     function shouldDeferIndexType(type: Type, indexFlags = IndexFlags.None) {
         return !!(type.flags & TypeFlags.InstantiableNonPrimitive ||
             isGenericTupleType(type) ||
-            isGenericMappedType(type) && (!hasDistributiveNameType(type) || getMappedTypeNameTypeKind(type) === MappedTypeNameTypeKind.Remapping) ||
+            isGenericMappedType(type) && (getHomomorphicTypeVariable(type.target as MappedType ?? type) && !getNameTypeFromMappedType(type) && getCombinedMappedTypeReadonlyness(type) || (!hasDistributiveNameType(type) || getMappedTypeNameTypeKind(type) === MappedTypeNameTypeKind.Remapping)) ||
             type.flags & TypeFlags.Union && !(indexFlags & IndexFlags.NoReducibleCheck) && isGenericReducibleType(type) ||
             type.flags & TypeFlags.Intersection && maybeTypeOfKind(type, TypeFlags.Instantiable) && some((type as IntersectionType).types, isEmptyAnonymousObjectType));
     }
diff --git a/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.symbols b/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.symbols
new file mode 100644
index 0000000000000..96fbef28a7d93
--- /dev/null
+++ b/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.symbols
@@ -0,0 +1,108 @@
+//// [tests/cases/compiler/indexTypeOnHomomorphicMappedTypesWithReadonly1.ts] ////
+
+=== indexTypeOnHomomorphicMappedTypesWithReadonly1.ts ===
+type T1 = Readonly<string[]>;
+>T1 : Symbol(T1, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 0, 0))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+
+type R1 = keyof T1; // keyof readonly string[]
+>R1 : Symbol(R1, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 0, 29))
+>T1 : Symbol(T1, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 0, 0))
+
+type KeyOfReadonly<T> = keyof Readonly<T>;
+>KeyOfReadonly : Symbol(KeyOfReadonly, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 1, 19))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 2, 19))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 2, 19))
+
+type R2 = KeyOfReadonly<string[]>; // keyof readonly string[]
+>R2 : Symbol(R2, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 2, 42))
+>KeyOfReadonly : Symbol(KeyOfReadonly, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 1, 19))
+
+type Identity<T> = { [K in keyof T]: T[K] };
+>Identity : Symbol(Identity, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 3, 34))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 14))
+>K : Symbol(K, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 22))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 14))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 14))
+>K : Symbol(K, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 22))
+
+type KeyOfReadonly2<T> = keyof Identity<Readonly<T>>; 
+>KeyOfReadonly2 : Symbol(KeyOfReadonly2, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 44))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 7, 20))
+>Identity : Symbol(Identity, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 3, 34))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 7, 20))
+
+type R3 = KeyOfReadonly2<string[]>; // keyof readonly string[]
+>R3 : Symbol(R3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 7, 53))
+>KeyOfReadonly2 : Symbol(KeyOfReadonly2, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 5, 44))
+
+type KeyOfReadonly3<T> = keyof Readonly<Identity<T>>; 
+>KeyOfReadonly3 : Symbol(KeyOfReadonly3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 8, 35))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 9, 20))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>Identity : Symbol(Identity, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 3, 34))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 9, 20))
+
+type R4 = KeyOfReadonly3<string[]>; // keyof readonly string[]
+>R4 : Symbol(R4, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 9, 53))
+>KeyOfReadonly3 : Symbol(KeyOfReadonly3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 8, 35))
+
+type Writable<T> = { -readonly [K in keyof T]: T[K] };
+>Writable : Symbol(Writable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 10, 35))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 14))
+>K : Symbol(K, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 32))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 14))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 14))
+>K : Symbol(K, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 32))
+
+type KeyOfWritable<T> = keyof Writable<T>;
+>KeyOfWritable : Symbol(KeyOfWritable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 54))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 14, 19))
+>Writable : Symbol(Writable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 10, 35))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 14, 19))
+
+type R5 = KeyOfWritable<readonly string[]>; // keyof string[]
+>R5 : Symbol(R5, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 14, 42))
+>KeyOfWritable : Symbol(KeyOfWritable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 12, 54))
+
+type KeyOfWritable2<T> = keyof Writable<Readonly<T>>;
+>KeyOfWritable2 : Symbol(KeyOfWritable2, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 15, 43))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 16, 20))
+>Writable : Symbol(Writable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 10, 35))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 16, 20))
+
+type R6 = KeyOfWritable2<readonly string[]>; // keyof string[]
+>R6 : Symbol(R6, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 16, 53))
+>KeyOfWritable2 : Symbol(KeyOfWritable2, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 15, 43))
+
+type KeyOfWritable3<T> = keyof Identity<Writable<Readonly<T>>>;
+>KeyOfWritable3 : Symbol(KeyOfWritable3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 17, 44))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 18, 20))
+>Identity : Symbol(Identity, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 3, 34))
+>Writable : Symbol(Writable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 10, 35))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 18, 20))
+
+type R7 = KeyOfWritable3<string[]>; // keyof string[]
+>R7 : Symbol(R7, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 18, 63))
+>KeyOfWritable3 : Symbol(KeyOfWritable3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 17, 44))
+
+type R8 = KeyOfWritable3<readonly string[]>; // keyof string[]
+>R8 : Symbol(R8, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 19, 35))
+>KeyOfWritable3 : Symbol(KeyOfWritable3, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 17, 44))
+
+type KeyOfReadonly4<T> = keyof Identity<Readonly<Writable<T>>>;
+>KeyOfReadonly4 : Symbol(KeyOfReadonly4, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 20, 44))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 22, 20))
+>Identity : Symbol(Identity, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 3, 34))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>Writable : Symbol(Writable, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 10, 35))
+>T : Symbol(T, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 22, 20))
+
+type R9 = KeyOfReadonly4<string[]>; // keyof readonly string[]
+>R9 : Symbol(R9, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 22, 63))
+>KeyOfReadonly4 : Symbol(KeyOfReadonly4, Decl(indexTypeOnHomomorphicMappedTypesWithReadonly1.ts, 20, 44))
+
diff --git a/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.types b/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.types
new file mode 100644
index 0000000000000..04cab26738129
--- /dev/null
+++ b/tests/baselines/reference/indexTypeOnHomomorphicMappedTypesWithReadonly1.types
@@ -0,0 +1,79 @@
+//// [tests/cases/compiler/indexTypeOnHomomorphicMappedTypesWithReadonly1.ts] ////
+
+=== indexTypeOnHomomorphicMappedTypesWithReadonly1.ts ===
+type T1 = Readonly<string[]>;
+>T1 : readonly string[]
+>   : ^^^^^^^^^^^^^^^^^
+
+type R1 = keyof T1; // keyof readonly string[]
+>R1 : keyof readonly string[]
+>   : ^^^^^^^^^^^^^^^^^^^^^^^
+
+type KeyOfReadonly<T> = keyof Readonly<T>;
+>KeyOfReadonly : keyof Readonly<T>
+>              : ^^^^^^^^^^^^^^^^^
+
+type R2 = KeyOfReadonly<string[]>; // keyof readonly string[]
+>R2 : keyof readonly string[]
+>   : ^^^^^^^^^^^^^^^^^^^^^^^
+
+type Identity<T> = { [K in keyof T]: T[K] };
+>Identity : Identity<T>
+>         : ^^^^^^^^^^^
+
+type KeyOfReadonly2<T> = keyof Identity<Readonly<T>>; 
+>KeyOfReadonly2 : keyof Identity<Readonly<T>>
+>               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+type R3 = KeyOfReadonly2<string[]>; // keyof readonly string[]
+>R3 : keyof readonly string[]
+>   : ^^^^^^^^^^^^^^^^^^^^^^^
+
+type KeyOfReadonly3<T> = keyof Readonly<Identity<T>>; 
+>KeyOfReadonly3 : keyof Readonly<Identity<T>>
+>               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+type R4 = KeyOfReadonly3<string[]>; // keyof readonly string[]
+>R4 : keyof readonly string[]
+>   : ^^^^^^^^^^^^^^^^^^^^^^^
+
+type Writable<T> = { -readonly [K in keyof T]: T[K] };
+>Writable : Writable<T>
+>         : ^^^^^^^^^^^
+
+type KeyOfWritable<T> = keyof Writable<T>;
+>KeyOfWritable : keyof Writable<T>
+>              : ^^^^^^^^^^^^^^^^^
+
+type R5 = KeyOfWritable<readonly string[]>; // keyof string[]
+>R5 : keyof string[]
+>   : ^^^^^^^^^^^^^^
+
+type KeyOfWritable2<T> = keyof Writable<Readonly<T>>;
+>KeyOfWritable2 : keyof Writable<Readonly<T>>
+>               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+type R6 = KeyOfWritable2<readonly string[]>; // keyof string[]
+>R6 : keyof string[]
+>   : ^^^^^^^^^^^^^^
+
+type KeyOfWritable3<T> = keyof Identity<Writable<Readonly<T>>>;
+>KeyOfWritable3 : keyof Identity<Writable<Readonly<T>>>
+>               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+type R7 = KeyOfWritable3<string[]>; // keyof string[]
+>R7 : keyof string[]
+>   : ^^^^^^^^^^^^^^
+
+type R8 = KeyOfWritable3<readonly string[]>; // keyof string[]
+>R8 : keyof string[]
+>   : ^^^^^^^^^^^^^^
+
+type KeyOfReadonly4<T> = keyof Identity<Readonly<Writable<T>>>;
+>KeyOfReadonly4 : keyof Identity<Readonly<Writable<T>>>
+>               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+type R9 = KeyOfReadonly4<string[]>; // keyof readonly string[]
+>R9 : keyof readonly string[]
+>   : ^^^^^^^^^^^^^^^^^^^^^^^
+
diff --git a/tests/cases/compiler/indexTypeOnHomomorphicMappedTypesWithReadonly1.ts b/tests/cases/compiler/indexTypeOnHomomorphicMappedTypesWithReadonly1.ts
new file mode 100644
index 0000000000000..fcbe2f345ae9e
--- /dev/null
+++ b/tests/cases/compiler/indexTypeOnHomomorphicMappedTypesWithReadonly1.ts
@@ -0,0 +1,27 @@
+// @strict: true
+// @noEmit: true
+
+type T1 = Readonly<string[]>;
+type R1 = keyof T1; // keyof readonly string[]
+type KeyOfReadonly<T> = keyof Readonly<T>;
+type R2 = KeyOfReadonly<string[]>; // keyof readonly string[]
+
+type Identity<T> = { [K in keyof T]: T[K] };
+
+type KeyOfReadonly2<T> = keyof Identity<Readonly<T>>; 
+type R3 = KeyOfReadonly2<string[]>; // keyof readonly string[]
+type KeyOfReadonly3<T> = keyof Readonly<Identity<T>>; 
+type R4 = KeyOfReadonly3<string[]>; // keyof readonly string[]
+
+type Writable<T> = { -readonly [K in keyof T]: T[K] };
+
+type KeyOfWritable<T> = keyof Writable<T>;
+type R5 = KeyOfWritable<readonly string[]>; // keyof string[]
+type KeyOfWritable2<T> = keyof Writable<Readonly<T>>;
+type R6 = KeyOfWritable2<readonly string[]>; // keyof string[]
+type KeyOfWritable3<T> = keyof Identity<Writable<Readonly<T>>>;
+type R7 = KeyOfWritable3<string[]>; // keyof string[]
+type R8 = KeyOfWritable3<readonly string[]>; // keyof string[]
+
+type KeyOfReadonly4<T> = keyof Identity<Readonly<Writable<T>>>;
+type R9 = KeyOfReadonly4<string[]>; // keyof readonly string[]