diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3d044fa5bf0f4..75fd291a681f9 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -14371,6 +14371,27 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return isTypeAssignableTo(nameType, getTypeParameterFromMappedType(type)) ? MappedTypeNameTypeKind.Filtering : MappedTypeNameTypeKind.Remapping;
     }
 
+    // generic mapped types that don't simplify or have a constraint still have a very simple set of keys - their nameType or constraintType.
+    // In many ways, this is a deferred version of what `getIndexTypeForMappedType` does to actually resolve the keys for _non_-generic types
+    function getGenericMappedTypeKeys(type: MappedType) {
+        const nameType = getNameTypeFromMappedType(type);
+        if (nameType && isMappedTypeWithKeyofConstraintDeclaration(type)) {
+            // we need to get the apparent mappings and union them with the generic mappings, since some properties may be
+            // missing from the `constraintType` which will otherwise be mapped in the object
+            const modifiersType = getApparentType(getModifiersTypeFromMappedType(type));
+            const mappedKeys: Type[] = [];
+            forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(
+                modifiersType,
+                TypeFlags.StringOrNumberLiteralOrUnique,
+                /*stringsOnly*/ false,
+                t => void mappedKeys.push(instantiateType(nameType, appendTypeMapping(type.mapper, getTypeParameterFromMappedType(type), t))),
+            );
+            // We still need to include the non-apparent (and thus still generic) keys since when this gets used in comparisons the other side might include them
+            return getUnionType([...mappedKeys, nameType]);
+        }
+        return nameType || getConstraintTypeFromMappedType(type);
+    }
+
     function resolveStructuredTypeMembers(type: StructuredType): ResolvedType {
         if (!(type as ResolvedType).members) {
             if (type.flags & TypeFlags.Object) {
diff --git a/tests/baselines/reference/keyRemappingKeyofResult.errors.txt b/tests/baselines/reference/keyRemappingKeyofResult.errors.txt
new file mode 100644
index 0000000000000..c92c299465e8b
--- /dev/null
+++ b/tests/baselines/reference/keyRemappingKeyofResult.errors.txt
@@ -0,0 +1,80 @@
+keyRemappingKeyofResult.ts(69,5): error TS2322: Type 'string' is not assignable to type 'keyof Remapped'.
+  Type '"whatever"' is not assignable to type 'unique symbol | "str" | DistributiveNonIndex<K>'.
+
+
+==== keyRemappingKeyofResult.ts (1 errors) ====
+    const sym = Symbol("")
+    type Orig = { [k: string]: any, str: any, [sym]: any }
+    
+    type Okay = Exclude<keyof Orig, never>
+    // type Okay = string | number | typeof sym
+    
+    type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
+    /* type Remapped = {
+        str: any;
+        [sym]: any;
+    } */
+    // no string index signature, right?
+    
+    type Oops = Exclude<keyof Remapped, never>
+    declare let x: Oops;
+    x = sym;
+    x = "str";
+    // type Oops = typeof sym <-- what happened to "str"?
+    
+    // equivalently, with an unresolved generic (no `exclude` shenanigans, since conditions won't execute):
+    function f<T>() {
+        type Orig = { [k: string]: any, str: any, [sym]: any } & T;
+        
+        type Okay = keyof Orig;
+        let a: Okay;
+        a = "str";
+        a = sym;
+        a = "whatever";
+        // type Okay = string | number | typeof sym
+        
+        type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
+        /* type Remapped = {
+            str: any;
+            [sym]: any;
+        } */
+        // no string index signature, right?
+        
+        type Oops = keyof Remapped;
+        let x: Oops;
+        x = sym;
+        x = "str";
+    }
+    
+    // and another generic case with a _distributive_ mapping, to trigger a different branch in `getIndexType`
+    function g<T>() {
+        type Orig = { [k: string]: any, str: any, [sym]: any } & T;
+        
+        type Okay = keyof Orig;
+        let a: Okay;
+        a = "str";
+        a = sym;
+        a = "whatever";
+        // type Okay = string | number | typeof sym
+    
+        type NonIndex<T extends PropertyKey> = {} extends Record<T, any> ? never : T;
+        type DistributiveNonIndex<T extends PropertyKey> = T extends unknown ? NonIndex<T> : never;
+        
+        type Remapped = { [K in keyof Orig as DistributiveNonIndex<K>]: any }
+        /* type Remapped = {
+            str: any;
+            [sym]: any;
+        } */
+        // no string index signature, right?
+        
+        type Oops = keyof Remapped;
+        let x: Oops;
+        x = sym;
+        x = "str";
+        x = "whatever"; // error
+        ~
+!!! error TS2322: Type 'string' is not assignable to type 'keyof Remapped'.
+!!! error TS2322:   Type '"whatever"' is not assignable to type 'unique symbol | "str" | DistributiveNonIndex<K>'.
+    }
+    
+    export {};
\ No newline at end of file
diff --git a/tests/baselines/reference/keyRemappingKeyofResult.js b/tests/baselines/reference/keyRemappingKeyofResult.js
index 3b51e02dc735e..9e4d1ea336c3f 100644
--- a/tests/baselines/reference/keyRemappingKeyofResult.js
+++ b/tests/baselines/reference/keyRemappingKeyofResult.js
@@ -69,6 +69,7 @@ function g<T>() {
     let x: Oops;
     x = sym;
     x = "str";
+    x = "whatever"; // error
 }
 
 export {};
@@ -97,5 +98,6 @@ function g() {
     let x;
     x = sym;
     x = "str";
+    x = "whatever"; // error
 }
 export {};
diff --git a/tests/baselines/reference/keyRemappingKeyofResult.symbols b/tests/baselines/reference/keyRemappingKeyofResult.symbols
index 722c000f268fa..3be5cf2460e84 100644
--- a/tests/baselines/reference/keyRemappingKeyofResult.symbols
+++ b/tests/baselines/reference/keyRemappingKeyofResult.symbols
@@ -190,6 +190,9 @@ function g<T>() {
 
     x = "str";
 >x : Symbol(x, Decl(keyRemappingKeyofResult.ts, 65, 7))
+
+    x = "whatever"; // error
+>x : Symbol(x, Decl(keyRemappingKeyofResult.ts, 65, 7))
 }
 
 export {};
diff --git a/tests/baselines/reference/keyRemappingKeyofResult.types b/tests/baselines/reference/keyRemappingKeyofResult.types
index 50949e385daa2..ce371fb30e5de 100644
--- a/tests/baselines/reference/keyRemappingKeyofResult.types
+++ b/tests/baselines/reference/keyRemappingKeyofResult.types
@@ -17,7 +17,9 @@ type Orig = { [k: string]: any, str: any, [sym]: any }
 >k : string
 >  : ^^^^^^
 >str : any
+>    : ^^^
 >[sym] : any
+>      : ^^^
 >sym : unique symbol
 >    : ^^^^^^^^^^^^^
 
@@ -74,7 +76,9 @@ function f<T>() {
 >k : string
 >  : ^^^^^^
 >str : any
+>    : ^^^
 >[sym] : any
+>      : ^^^
 >sym : unique symbol
 >    : ^^^^^^^^^^^^^
     
@@ -158,7 +162,9 @@ function g<T>() {
 >k : string
 >  : ^^^^^^
 >str : any
+>    : ^^^
 >[sym] : any
+>      : ^^^
 >sym : unique symbol
 >    : ^^^^^^^^^^^^^
     
@@ -237,6 +243,14 @@ function g<T>() {
 >  : ^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 >"str" : "str"
 >      : ^^^^^
+
+    x = "whatever"; // error
+>x = "whatever" : "whatever"
+>               : ^^^^^^^^^^
+>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }
+>  : ^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>"whatever" : "whatever"
+>           : ^^^^^^^^^^
 }
 
 export {};
diff --git a/tests/baselines/reference/keyRemappingKeyofResult2.errors.txt b/tests/baselines/reference/keyRemappingKeyofResult2.errors.txt
new file mode 100644
index 0000000000000..6ee25e23d479a
--- /dev/null
+++ b/tests/baselines/reference/keyRemappingKeyofResult2.errors.txt
@@ -0,0 +1,51 @@
+keyRemappingKeyofResult2.ts(23,7): error TS2344: Type 'Values<{ [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }>' does not satisfy the constraint 'ProvidedActor'.
+  Types of property 'src' are incompatible.
+    Type 'keyof { [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }' is not assignable to type 'string'.
+      Type 'string | number | symbol' is not assignable to type 'string'.
+        Type 'number' is not assignable to type 'string'.
+
+
+==== keyRemappingKeyofResult2.ts (1 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/56239
+    
+    type Values<T> = T[keyof T];
+    
+    type ProvidedActor = {
+      src: string;
+      logic: unknown;
+    };
+    
+    interface StateMachineConfig<TActors extends ProvidedActor> {
+      invoke: {
+        src: TActors["src"];
+      };
+    }
+    
+    declare function setup<TActors extends Record<string, unknown>>(_: {
+      actors: {
+        [K in keyof TActors]: TActors[K];
+      };
+    }): {
+      createMachine: (
+        config: StateMachineConfig<
+          Values<{
+          ~~~~~~~~
+            [K in keyof TActors as K & string]: {
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+              src: K;
+    ~~~~~~~~~~~~~~~~~
+              logic: TActors[K];
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+            };
+    ~~~~~~~~~~
+          }>
+    ~~~~~~~~
+!!! error TS2344: Type 'Values<{ [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }>' does not satisfy the constraint 'ProvidedActor'.
+!!! error TS2344:   Types of property 'src' are incompatible.
+!!! error TS2344:     Type 'keyof { [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }' is not assignable to type 'string'.
+!!! error TS2344:       Type 'string | number | symbol' is not assignable to type 'string'.
+!!! error TS2344:         Type 'number' is not assignable to type 'string'.
+        >,
+      ) => void;
+    };
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/keyRemappingKeyofResult2.symbols b/tests/baselines/reference/keyRemappingKeyofResult2.symbols
new file mode 100644
index 0000000000000..b3fd16667f89f
--- /dev/null
+++ b/tests/baselines/reference/keyRemappingKeyofResult2.symbols
@@ -0,0 +1,84 @@
+//// [tests/cases/compiler/keyRemappingKeyofResult2.ts] ////
+
+=== keyRemappingKeyofResult2.ts ===
+// https://github.com/microsoft/TypeScript/issues/56239
+
+type Values<T> = T[keyof T];
+>Values : Symbol(Values, Decl(keyRemappingKeyofResult2.ts, 0, 0))
+>T : Symbol(T, Decl(keyRemappingKeyofResult2.ts, 2, 12))
+>T : Symbol(T, Decl(keyRemappingKeyofResult2.ts, 2, 12))
+>T : Symbol(T, Decl(keyRemappingKeyofResult2.ts, 2, 12))
+
+type ProvidedActor = {
+>ProvidedActor : Symbol(ProvidedActor, Decl(keyRemappingKeyofResult2.ts, 2, 28))
+
+  src: string;
+>src : Symbol(src, Decl(keyRemappingKeyofResult2.ts, 4, 22))
+
+  logic: unknown;
+>logic : Symbol(logic, Decl(keyRemappingKeyofResult2.ts, 5, 14))
+
+};
+
+interface StateMachineConfig<TActors extends ProvidedActor> {
+>StateMachineConfig : Symbol(StateMachineConfig, Decl(keyRemappingKeyofResult2.ts, 7, 2))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 9, 29))
+>ProvidedActor : Symbol(ProvidedActor, Decl(keyRemappingKeyofResult2.ts, 2, 28))
+
+  invoke: {
+>invoke : Symbol(StateMachineConfig.invoke, Decl(keyRemappingKeyofResult2.ts, 9, 61))
+
+    src: TActors["src"];
+>src : Symbol(src, Decl(keyRemappingKeyofResult2.ts, 10, 11))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 9, 29))
+
+  };
+}
+
+declare function setup<TActors extends Record<string, unknown>>(_: {
+>setup : Symbol(setup, Decl(keyRemappingKeyofResult2.ts, 13, 1))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 15, 23))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>_ : Symbol(_, Decl(keyRemappingKeyofResult2.ts, 15, 64))
+
+  actors: {
+>actors : Symbol(actors, Decl(keyRemappingKeyofResult2.ts, 15, 68))
+
+    [K in keyof TActors]: TActors[K];
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 17, 5))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 15, 23))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 15, 23))
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 17, 5))
+
+  };
+}): {
+  createMachine: (
+>createMachine : Symbol(createMachine, Decl(keyRemappingKeyofResult2.ts, 19, 5))
+
+    config: StateMachineConfig<
+>config : Symbol(config, Decl(keyRemappingKeyofResult2.ts, 20, 18))
+>StateMachineConfig : Symbol(StateMachineConfig, Decl(keyRemappingKeyofResult2.ts, 7, 2))
+
+      Values<{
+>Values : Symbol(Values, Decl(keyRemappingKeyofResult2.ts, 0, 0))
+
+        [K in keyof TActors as K & string]: {
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 23, 9))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 15, 23))
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 23, 9))
+
+          src: K;
+>src : Symbol(src, Decl(keyRemappingKeyofResult2.ts, 23, 45))
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 23, 9))
+
+          logic: TActors[K];
+>logic : Symbol(logic, Decl(keyRemappingKeyofResult2.ts, 24, 17))
+>TActors : Symbol(TActors, Decl(keyRemappingKeyofResult2.ts, 15, 23))
+>K : Symbol(K, Decl(keyRemappingKeyofResult2.ts, 23, 9))
+
+        };
+      }>
+    >,
+  ) => void;
+};
+
diff --git a/tests/baselines/reference/keyRemappingKeyofResult2.types b/tests/baselines/reference/keyRemappingKeyofResult2.types
new file mode 100644
index 0000000000000..b65ebbf5b6a0e
--- /dev/null
+++ b/tests/baselines/reference/keyRemappingKeyofResult2.types
@@ -0,0 +1,72 @@
+//// [tests/cases/compiler/keyRemappingKeyofResult2.ts] ////
+
+=== keyRemappingKeyofResult2.ts ===
+// https://github.com/microsoft/TypeScript/issues/56239
+
+type Values<T> = T[keyof T];
+>Values : Values<T>
+>       : ^^^^^^^^^
+
+type ProvidedActor = {
+>ProvidedActor : ProvidedActor
+>              : ^^^^^^^^^^^^^
+
+  src: string;
+>src : string
+>    : ^^^^^^
+
+  logic: unknown;
+>logic : unknown
+>      : ^^^^^^^
+
+};
+
+interface StateMachineConfig<TActors extends ProvidedActor> {
+  invoke: {
+>invoke : { src: TActors["src"]; }
+>       : ^^^^^^^              ^^^
+
+    src: TActors["src"];
+>src : TActors["src"]
+>    : ^^^^^^^^^^^^^^
+
+  };
+}
+
+declare function setup<TActors extends Record<string, unknown>>(_: {
+>setup : <TActors extends Record<string, unknown>>(_: { actors: { [K in keyof TActors]: TActors[K]; }; }) => { createMachine: (config: StateMachineConfig<Values<{ [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }>>) => void; }
+>      : ^       ^^^^^^^^^                       ^^ ^^                                                  ^^^^^                                                                                                                                         
+>_ : { actors: { [K in keyof TActors]: TActors[K]; }; }
+>  : ^^^^^^^^^^                                     ^^^
+
+  actors: {
+>actors : { [K in keyof TActors]: TActors[K]; }
+>       : ^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+    [K in keyof TActors]: TActors[K];
+  };
+}): {
+  createMachine: (
+>createMachine : (config: StateMachineConfig<Values<{ [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }>>) => void
+>              : ^      ^^                                                                                                   ^^^^^    
+
+    config: StateMachineConfig<
+>config : StateMachineConfig<Values<{ [K in keyof TActors as K & string]: { src: K; logic: TActors[K]; }; }>>
+>       : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^          ^^^^^^^^
+
+      Values<{
+        [K in keyof TActors as K & string]: {
+          src: K;
+>src : K
+>    : ^
+
+          logic: TActors[K];
+>logic : TActors[K]
+>      : ^^^^^^^^^^
+
+        };
+      }>
+    >,
+  ) => void;
+};
+
diff --git a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.js b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.js
index a73af0b42ab1f..ff8728571aa47 100644
--- a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.js
+++ b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.js
@@ -10,9 +10,6 @@ type Str<T extends string> = T
 type Bar<T> = 
   T extends Foo
     ? T['foo'] extends string
-      // Type 'T["foo"]' does not satisfy the constraint 'string'.
-      //  Type 'string | undefined' is not assignable to type 'string'.
-      //   Type 'undefined' is not assignable to type 'string'.(2344)
       ? Str<T['foo']>
       : never
     : never
diff --git a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.symbols b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.symbols
index fc2995682b466..f9e6e9a2ce0fa 100644
--- a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.symbols
+++ b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.symbols
@@ -24,9 +24,6 @@ type Bar<T> =
     ? T['foo'] extends string
 >T : Symbol(T, Decl(substitutionTypeForIndexedAccessType2.ts, 6, 9))
 
-      // Type 'T["foo"]' does not satisfy the constraint 'string'.
-      //  Type 'string | undefined' is not assignable to type 'string'.
-      //   Type 'undefined' is not assignable to type 'string'.(2344)
       ? Str<T['foo']>
 >Str : Symbol(Str, Decl(substitutionTypeForIndexedAccessType2.ts, 2, 1))
 >T : Symbol(T, Decl(substitutionTypeForIndexedAccessType2.ts, 6, 9))
diff --git a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.types b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.types
index 4567d59489a15..d303e54936727 100644
--- a/tests/baselines/reference/substitutionTypeForIndexedAccessType2.types
+++ b/tests/baselines/reference/substitutionTypeForIndexedAccessType2.types
@@ -17,9 +17,6 @@ type Bar<T> =
 
   T extends Foo
     ? T['foo'] extends string
-      // Type 'T["foo"]' does not satisfy the constraint 'string'.
-      //  Type 'string | undefined' is not assignable to type 'string'.
-      //   Type 'undefined' is not assignable to type 'string'.(2344)
       ? Str<T['foo']>
       : never
     : never
diff --git a/tests/cases/compiler/keyRemappingKeyofResult.ts b/tests/cases/compiler/keyRemappingKeyofResult.ts
index fcf3f835ac691..ba0b0939ae3cb 100644
--- a/tests/cases/compiler/keyRemappingKeyofResult.ts
+++ b/tests/cases/compiler/keyRemappingKeyofResult.ts
@@ -67,6 +67,7 @@ function g<T>() {
     let x: Oops;
     x = sym;
     x = "str";
+    x = "whatever"; // error
 }
 
 export {};
\ No newline at end of file
diff --git a/tests/cases/compiler/keyRemappingKeyofResult2.ts b/tests/cases/compiler/keyRemappingKeyofResult2.ts
new file mode 100644
index 0000000000000..b77b7af1760a9
--- /dev/null
+++ b/tests/cases/compiler/keyRemappingKeyofResult2.ts
@@ -0,0 +1,34 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/56239
+
+type Values<T> = T[keyof T];
+
+type ProvidedActor = {
+  src: string;
+  logic: unknown;
+};
+
+interface StateMachineConfig<TActors extends ProvidedActor> {
+  invoke: {
+    src: TActors["src"];
+  };
+}
+
+declare function setup<TActors extends Record<string, unknown>>(_: {
+  actors: {
+    [K in keyof TActors]: TActors[K];
+  };
+}): {
+  createMachine: (
+    config: StateMachineConfig<
+      Values<{
+        [K in keyof TActors as K & string]: {
+          src: K;
+          logic: TActors[K];
+        };
+      }>
+    >,
+  ) => void;
+};
diff --git a/tests/cases/compiler/substitutionTypeForIndexedAccessType2.ts b/tests/cases/compiler/substitutionTypeForIndexedAccessType2.ts
index c687879efd463..97c0f6f538db5 100644
--- a/tests/cases/compiler/substitutionTypeForIndexedAccessType2.ts
+++ b/tests/cases/compiler/substitutionTypeForIndexedAccessType2.ts
@@ -7,9 +7,6 @@ type Str<T extends string> = T
 type Bar<T> = 
   T extends Foo
     ? T['foo'] extends string
-      // Type 'T["foo"]' does not satisfy the constraint 'string'.
-      //  Type 'string | undefined' is not assignable to type 'string'.
-      //   Type 'undefined' is not assignable to type 'string'.(2344)
       ? Str<T['foo']>
       : never
     : never
\ No newline at end of file