diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f36f471ee75..00498191f28 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -3973,7 +3973,7 @@ namespace ts {
                 return true;
             }
             if (type.flags & TypeFlags.TypeVariable) {
-                const constraint = getBaseConstraintOfType(<TypeVariable>type);
+                const constraint = getBaseConstraintOfType(type);
                 return constraint && isValidBaseType(constraint) && isMixinConstructorType(constraint);
             }
             return false;
@@ -4989,16 +4989,32 @@ namespace ts {
         }
 
         function getConstraintOfType(type: TypeVariable | UnionOrIntersectionType): Type {
-            return type.flags & TypeFlags.TypeParameter ? getConstraintOfTypeParameter(<TypeParameter>type) : getBaseConstraintOfType(type);
+            return type.flags & TypeFlags.TypeParameter ? getConstraintOfTypeParameter(<TypeParameter>type) :
+                type.flags & TypeFlags.IndexedAccess ? getConstraintOfIndexedAccess(<IndexedAccessType>type) :
+                getBaseConstraintOfType(type);
         }
 
         function getConstraintOfTypeParameter(typeParameter: TypeParameter): Type {
             return hasNonCircularBaseConstraint(typeParameter) ? getConstraintFromTypeParameter(typeParameter) : undefined;
         }
 
-        function getBaseConstraintOfType(type: TypeVariable | UnionOrIntersectionType): Type {
-            const constraint = getResolvedBaseConstraint(type);
-            return constraint !== noConstraintType && constraint !== circularConstraintType ? constraint : undefined;
+        function getConstraintOfIndexedAccess(type: IndexedAccessType) {
+            const baseObjectType = getBaseConstraintOfType(type.objectType);
+            const baseIndexType = getBaseConstraintOfType(type.indexType);
+            return baseObjectType || baseIndexType ? getIndexedAccessType(baseObjectType || type.objectType, baseIndexType || type.indexType) : undefined;
+        }
+
+        function getBaseConstraintOfType(type: Type): Type {
+            if (type.flags & (TypeFlags.TypeVariable | TypeFlags.UnionOrIntersection)) {
+                const constraint = getResolvedBaseConstraint(<TypeVariable | UnionOrIntersectionType>type);
+                if (constraint !== noConstraintType && constraint !== circularConstraintType) {
+                    return constraint;
+                }
+            }
+            else if (type.flags & TypeFlags.Index) {
+                return stringType;
+            }
+            return undefined;
         }
 
         function hasNonCircularBaseConstraint(type: TypeVariable): boolean {
@@ -5096,7 +5112,7 @@ namespace ts {
          * type itself. Note that the apparent type of a union type is the union type itself.
          */
         function getApparentType(type: Type): Type {
-            const t = type.flags & TypeFlags.TypeVariable ? getBaseConstraintOfType(<TypeVariable>type) || emptyObjectType : type;
+            const t = type.flags & TypeFlags.TypeVariable ? getBaseConstraintOfType(type) || emptyObjectType : type;
             return t.flags & TypeFlags.Intersection ? getApparentTypeOfIntersectionType(<IntersectionType>t) :
                 t.flags & TypeFlags.StringLike ? globalStringType :
                 t.flags & TypeFlags.NumberLike ? globalNumberType :
@@ -7921,7 +7937,7 @@ namespace ts {
                     }
                     // A type S is related to a type T[K] if S is related to A[K], where K is string-like and
                     // A is the apparent type of S.
-                    const constraint = getBaseConstraintOfType(<IndexedAccessType>target);
+                    const constraint = getBaseConstraintOfType(target);
                     if (constraint) {
                         if (result = isRelatedTo(source, constraint, reportErrors)) {
                             errorInfo = saveErrorInfo;
@@ -7961,7 +7977,7 @@ namespace ts {
                 else if (source.flags & TypeFlags.IndexedAccess) {
                     // A type S[K] is related to a type T if A[K] is related to T, where K is string-like and
                     // A is the apparent type of S.
-                    const constraint = getBaseConstraintOfType(<IndexedAccessType>source);
+                    const constraint = getConstraintOfType(<IndexedAccessType>source);
                     if (constraint) {
                         if (result = isRelatedTo(constraint, target, reportErrors)) {
                             errorInfo = saveErrorInfo;
@@ -9874,7 +9890,7 @@ namespace ts {
                 return strictNullChecks ? TypeFacts.ObjectStrictFacts : TypeFacts.ObjectFacts;
             }
             if (flags & TypeFlags.TypeVariable) {
-                return getTypeFacts(getBaseConstraintOfType(<TypeVariable>type) || emptyObjectType);
+                return getTypeFacts(getBaseConstraintOfType(type) || emptyObjectType);
             }
             if (flags & TypeFlags.UnionOrIntersection) {
                 return getTypeFactsOfTypes((<UnionOrIntersectionType>type).types);
@@ -10686,7 +10702,7 @@ namespace ts {
                             return targetType;
                         }
                         if (type.flags & TypeFlags.TypeVariable) {
-                            const constraint = getBaseConstraintOfType(<TypeVariable>type) || anyType;
+                            const constraint = getBaseConstraintOfType(type) || anyType;
                             if (isTypeSubtypeOf(targetType, constraint)) {
                                 return getIntersectionType([type, targetType]);
                             }
@@ -16234,7 +16250,7 @@ namespace ts {
         function isLiteralContextualType(contextualType: Type) {
             if (contextualType) {
                 if (contextualType.flags & TypeFlags.TypeVariable) {
-                    const constraint = getBaseConstraintOfType(<TypeVariable>contextualType) || emptyObjectType;
+                    const constraint = getBaseConstraintOfType(contextualType) || emptyObjectType;
                     // If the type parameter is constrained to the base primitive type we're checking for,
                     // consider this a literal context. For example, given a type parameter 'T extends string',
                     // this causes us to infer string literal types for T.
@@ -17124,7 +17140,7 @@ namespace ts {
             // Check if we're indexing with a numeric type and the object type is a generic
             // type with a constraint that has a numeric index signature.
             if (maybeTypeOfKind(objectType, TypeFlags.TypeVariable) && isTypeOfKind(indexType, TypeFlags.NumberLike)) {
-                const constraint = getBaseConstraintOfType(<TypeVariable | UnionOrIntersectionType>objectType);
+                const constraint = getBaseConstraintOfType(objectType);
                 if (constraint && getIndexInfoOfType(constraint, IndexKind.Number)) {
                     return type;
                 }
diff --git a/tests/baselines/reference/indexedAccessTypeConstraints.js b/tests/baselines/reference/indexedAccessTypeConstraints.js
new file mode 100644
index 00000000000..ec9af906e43
--- /dev/null
+++ b/tests/baselines/reference/indexedAccessTypeConstraints.js
@@ -0,0 +1,86 @@
+//// [indexedAccessTypeConstraints.ts]
+
+// Repro from #14557
+
+interface IData<T> {
+    content: T;
+}
+
+type Data<T> = {
+    get: <K extends keyof T>(prop: K) => T[K];
+};
+
+class Parent<M> {
+    private data: Data<M>;
+    getData(): Data<M> {
+        return this.data;
+    }
+}
+
+export class Foo<C> extends Parent<IData<C>> {
+    getContent(): C {
+        return this.getData().get('content');
+    }
+}
+
+export class Bar<C, T extends IData<C>> extends Parent<T> {
+    getContent(): C {
+        return this.getData().get('content');
+    }
+}
+
+// Repro from #14557
+
+function foo<C, T extends { content: C }>(x: C, y: T['content']) {
+    x = y;
+}
+
+
+//// [indexedAccessTypeConstraints.js]
+// Repro from #14557
+"use strict";
+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = Object.setPrototypeOf ||
+        ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+        function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
+    return function (d, b) {
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
+exports.__esModule = true;
+var Parent = (function () {
+    function Parent() {
+    }
+    Parent.prototype.getData = function () {
+        return this.data;
+    };
+    return Parent;
+}());
+var Foo = (function (_super) {
+    __extends(Foo, _super);
+    function Foo() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    Foo.prototype.getContent = function () {
+        return this.getData().get('content');
+    };
+    return Foo;
+}(Parent));
+exports.Foo = Foo;
+var Bar = (function (_super) {
+    __extends(Bar, _super);
+    function Bar() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    Bar.prototype.getContent = function () {
+        return this.getData().get('content');
+    };
+    return Bar;
+}(Parent));
+exports.Bar = Bar;
+// Repro from #14557
+function foo(x, y) {
+    x = y;
+}
diff --git a/tests/baselines/reference/indexedAccessTypeConstraints.symbols b/tests/baselines/reference/indexedAccessTypeConstraints.symbols
new file mode 100644
index 00000000000..b2d10c7ee27
--- /dev/null
+++ b/tests/baselines/reference/indexedAccessTypeConstraints.symbols
@@ -0,0 +1,109 @@
+=== tests/cases/compiler/indexedAccessTypeConstraints.ts ===
+
+// Repro from #14557
+
+interface IData<T> {
+>IData : Symbol(IData, Decl(indexedAccessTypeConstraints.ts, 0, 0))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 3, 16))
+
+    content: T;
+>content : Symbol(IData.content, Decl(indexedAccessTypeConstraints.ts, 3, 20))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 3, 16))
+}
+
+type Data<T> = {
+>Data : Symbol(Data, Decl(indexedAccessTypeConstraints.ts, 5, 1))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 7, 10))
+
+    get: <K extends keyof T>(prop: K) => T[K];
+>get : Symbol(get, Decl(indexedAccessTypeConstraints.ts, 7, 16))
+>K : Symbol(K, Decl(indexedAccessTypeConstraints.ts, 8, 10))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 7, 10))
+>prop : Symbol(prop, Decl(indexedAccessTypeConstraints.ts, 8, 29))
+>K : Symbol(K, Decl(indexedAccessTypeConstraints.ts, 8, 10))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 7, 10))
+>K : Symbol(K, Decl(indexedAccessTypeConstraints.ts, 8, 10))
+
+};
+
+class Parent<M> {
+>Parent : Symbol(Parent, Decl(indexedAccessTypeConstraints.ts, 9, 2))
+>M : Symbol(M, Decl(indexedAccessTypeConstraints.ts, 11, 13))
+
+    private data: Data<M>;
+>data : Symbol(Parent.data, Decl(indexedAccessTypeConstraints.ts, 11, 17))
+>Data : Symbol(Data, Decl(indexedAccessTypeConstraints.ts, 5, 1))
+>M : Symbol(M, Decl(indexedAccessTypeConstraints.ts, 11, 13))
+
+    getData(): Data<M> {
+>getData : Symbol(Parent.getData, Decl(indexedAccessTypeConstraints.ts, 12, 26))
+>Data : Symbol(Data, Decl(indexedAccessTypeConstraints.ts, 5, 1))
+>M : Symbol(M, Decl(indexedAccessTypeConstraints.ts, 11, 13))
+
+        return this.data;
+>this.data : Symbol(Parent.data, Decl(indexedAccessTypeConstraints.ts, 11, 17))
+>this : Symbol(Parent, Decl(indexedAccessTypeConstraints.ts, 9, 2))
+>data : Symbol(Parent.data, Decl(indexedAccessTypeConstraints.ts, 11, 17))
+    }
+}
+
+export class Foo<C> extends Parent<IData<C>> {
+>Foo : Symbol(Foo, Decl(indexedAccessTypeConstraints.ts, 16, 1))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 18, 17))
+>Parent : Symbol(Parent, Decl(indexedAccessTypeConstraints.ts, 9, 2))
+>IData : Symbol(IData, Decl(indexedAccessTypeConstraints.ts, 0, 0))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 18, 17))
+
+    getContent(): C {
+>getContent : Symbol(Foo.getContent, Decl(indexedAccessTypeConstraints.ts, 18, 46))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 18, 17))
+
+        return this.getData().get('content');
+>this.getData().get : Symbol(get, Decl(indexedAccessTypeConstraints.ts, 7, 16))
+>this.getData : Symbol(Parent.getData, Decl(indexedAccessTypeConstraints.ts, 12, 26))
+>this : Symbol(Foo, Decl(indexedAccessTypeConstraints.ts, 16, 1))
+>getData : Symbol(Parent.getData, Decl(indexedAccessTypeConstraints.ts, 12, 26))
+>get : Symbol(get, Decl(indexedAccessTypeConstraints.ts, 7, 16))
+    }
+}
+
+export class Bar<C, T extends IData<C>> extends Parent<T> {
+>Bar : Symbol(Bar, Decl(indexedAccessTypeConstraints.ts, 22, 1))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 24, 17))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 24, 19))
+>IData : Symbol(IData, Decl(indexedAccessTypeConstraints.ts, 0, 0))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 24, 17))
+>Parent : Symbol(Parent, Decl(indexedAccessTypeConstraints.ts, 9, 2))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 24, 19))
+
+    getContent(): C {
+>getContent : Symbol(Bar.getContent, Decl(indexedAccessTypeConstraints.ts, 24, 59))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 24, 17))
+
+        return this.getData().get('content');
+>this.getData().get : Symbol(get, Decl(indexedAccessTypeConstraints.ts, 7, 16))
+>this.getData : Symbol(Parent.getData, Decl(indexedAccessTypeConstraints.ts, 12, 26))
+>this : Symbol(Bar, Decl(indexedAccessTypeConstraints.ts, 22, 1))
+>getData : Symbol(Parent.getData, Decl(indexedAccessTypeConstraints.ts, 12, 26))
+>get : Symbol(get, Decl(indexedAccessTypeConstraints.ts, 7, 16))
+    }
+}
+
+// Repro from #14557
+
+function foo<C, T extends { content: C }>(x: C, y: T['content']) {
+>foo : Symbol(foo, Decl(indexedAccessTypeConstraints.ts, 28, 1))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 32, 13))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 32, 15))
+>content : Symbol(content, Decl(indexedAccessTypeConstraints.ts, 32, 27))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 32, 13))
+>x : Symbol(x, Decl(indexedAccessTypeConstraints.ts, 32, 42))
+>C : Symbol(C, Decl(indexedAccessTypeConstraints.ts, 32, 13))
+>y : Symbol(y, Decl(indexedAccessTypeConstraints.ts, 32, 47))
+>T : Symbol(T, Decl(indexedAccessTypeConstraints.ts, 32, 15))
+
+    x = y;
+>x : Symbol(x, Decl(indexedAccessTypeConstraints.ts, 32, 42))
+>y : Symbol(y, Decl(indexedAccessTypeConstraints.ts, 32, 47))
+}
+
diff --git a/tests/baselines/reference/indexedAccessTypeConstraints.types b/tests/baselines/reference/indexedAccessTypeConstraints.types
new file mode 100644
index 00000000000..5a2cbc4933f
--- /dev/null
+++ b/tests/baselines/reference/indexedAccessTypeConstraints.types
@@ -0,0 +1,116 @@
+=== tests/cases/compiler/indexedAccessTypeConstraints.ts ===
+
+// Repro from #14557
+
+interface IData<T> {
+>IData : IData<T>
+>T : T
+
+    content: T;
+>content : T
+>T : T
+}
+
+type Data<T> = {
+>Data : { get: <K extends keyof T>(prop: K) => T[K]; }
+>T : T
+
+    get: <K extends keyof T>(prop: K) => T[K];
+>get : <K extends keyof T>(prop: K) => T[K]
+>K : K
+>T : T
+>prop : K
+>K : K
+>T : T
+>K : K
+
+};
+
+class Parent<M> {
+>Parent : Parent<M>
+>M : M
+
+    private data: Data<M>;
+>data : { get: <K extends keyof M>(prop: K) => M[K]; }
+>Data : { get: <K extends keyof T>(prop: K) => T[K]; }
+>M : M
+
+    getData(): Data<M> {
+>getData : () => { get: <K extends keyof M>(prop: K) => M[K]; }
+>Data : { get: <K extends keyof T>(prop: K) => T[K]; }
+>M : M
+
+        return this.data;
+>this.data : { get: <K extends keyof M>(prop: K) => M[K]; }
+>this : this
+>data : { get: <K extends keyof M>(prop: K) => M[K]; }
+    }
+}
+
+export class Foo<C> extends Parent<IData<C>> {
+>Foo : Foo<C>
+>C : C
+>Parent : Parent<IData<C>>
+>IData : IData<T>
+>C : C
+
+    getContent(): C {
+>getContent : () => C
+>C : C
+
+        return this.getData().get('content');
+>this.getData().get('content') : C
+>this.getData().get : <K extends "content">(prop: K) => IData<C>[K]
+>this.getData() : { get: <K extends "content">(prop: K) => IData<C>[K]; }
+>this.getData : () => { get: <K extends "content">(prop: K) => IData<C>[K]; }
+>this : this
+>getData : () => { get: <K extends "content">(prop: K) => IData<C>[K]; }
+>get : <K extends "content">(prop: K) => IData<C>[K]
+>'content' : "content"
+    }
+}
+
+export class Bar<C, T extends IData<C>> extends Parent<T> {
+>Bar : Bar<C, T>
+>C : C
+>T : T
+>IData : IData<T>
+>C : C
+>Parent : Parent<T>
+>T : T
+
+    getContent(): C {
+>getContent : () => C
+>C : C
+
+        return this.getData().get('content');
+>this.getData().get('content') : T["content"]
+>this.getData().get : <K extends keyof T>(prop: K) => T[K]
+>this.getData() : { get: <K extends keyof T>(prop: K) => T[K]; }
+>this.getData : () => { get: <K extends keyof T>(prop: K) => T[K]; }
+>this : this
+>getData : () => { get: <K extends keyof T>(prop: K) => T[K]; }
+>get : <K extends keyof T>(prop: K) => T[K]
+>'content' : "content"
+    }
+}
+
+// Repro from #14557
+
+function foo<C, T extends { content: C }>(x: C, y: T['content']) {
+>foo : <C, T extends { content: C; }>(x: C, y: T["content"]) => void
+>C : C
+>T : T
+>content : C
+>C : C
+>x : C
+>C : C
+>y : T["content"]
+>T : T
+
+    x = y;
+>x = y : T["content"]
+>x : C
+>y : T["content"]
+}
+
diff --git a/tests/baselines/reference/mappedTypeRelationships.errors.txt b/tests/baselines/reference/mappedTypeRelationships.errors.txt
index 22f56dacaf6..bc26bb272f5 100644
--- a/tests/baselines/reference/mappedTypeRelationships.errors.txt
+++ b/tests/baselines/reference/mappedTypeRelationships.errors.txt
@@ -1,14 +1,18 @@
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(12,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
-  Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[keyof T]'.
+    Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(17,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
-  Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[K]'.
+    Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(21,5): error TS2536: Type 'keyof U' cannot be used to index type 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(22,5): error TS2322: Type 'T[keyof U]' is not assignable to type 'U[keyof U]'.
-  Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[keyof U]'.
+    Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(22,12): error TS2536: Type 'keyof U' cannot be used to index type 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(26,5): error TS2536: Type 'K' cannot be used to index type 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(27,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
-  Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[K]'.
+    Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(27,12): error TS2536: Type 'K' cannot be used to index type 'T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(31,5): error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
   Type 'undefined' is not assignable to type 'T[keyof T]'.
@@ -17,13 +21,19 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(36,5): error TS2
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(41,5): error TS2322: Type 'U[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
   Type 'undefined' is not assignable to type 'T[keyof T]'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(42,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
-  Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
-    Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
+    Type 'T[string]' is not assignable to type 'U[keyof T]'.
+      Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
+        Type 'T[string]' is not assignable to type 'U[keyof T]'.
+          Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(46,5): error TS2322: Type 'U[K] | undefined' is not assignable to type 'T[K]'.
   Type 'undefined' is not assignable to type 'T[K]'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(47,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K] | undefined'.
-  Type 'T[K]' is not assignable to type 'U[K]'.
-    Type 'T' is not assignable to type 'U'.
+  Type 'T[string]' is not assignable to type 'U[K] | undefined'.
+    Type 'T[string]' is not assignable to type 'U[K]'.
+      Type 'T[K]' is not assignable to type 'U[K]'.
+        Type 'T[string]' is not assignable to type 'U[K]'.
+          Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(52,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(57,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(62,5): error TS2542: Index signature in type 'Readonly<U>' only permits reading.
@@ -33,7 +43,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(76,5): error TS2
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(126,5): error TS2322: Type 'Partial<U>' is not assignable to type 'Identity<U>'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(142,5): error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
   Type 'T[P]' is not assignable to type 'U[P]'.
-    Type 'T' is not assignable to type 'U'.
+    Type 'T[string]' is not assignable to type 'U[P]'.
+      Type 'T' is not assignable to type 'U'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(147,5): error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof U]: U[P]; }'.
   Type 'keyof U' is not assignable to type 'keyof T'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(152,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof T]: T[P]; }'.
@@ -44,7 +55,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(162,5): error TS
   Type 'keyof T' is not assignable to type 'K'.
 tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in K]: U[P]; }'.
   Type 'T[P]' is not assignable to type 'U[P]'.
-    Type 'T' is not assignable to type 'U'.
+    Type 'T[string]' is not assignable to type 'U[P]'.
+      Type 'T' is not assignable to type 'U'.
 
 
 ==== tests/cases/conformance/types/mapped/mappedTypeRelationships.ts (27 errors) ====
@@ -62,7 +74,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
-!!! error TS2322:   Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[keyof T]'.
+!!! error TS2322:     Type 'T' is not assignable to type 'U'.
     }
     
     function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K) {
@@ -70,7 +83,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
-!!! error TS2322:   Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[K]'.
+!!! error TS2322:     Type 'T' is not assignable to type 'U'.
     }
     
     function f5<T, U extends T>(x: T, y: U, k: keyof U) {
@@ -80,7 +94,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[keyof U]' is not assignable to type 'U[keyof U]'.
-!!! error TS2322:   Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[keyof U]'.
+!!! error TS2322:     Type 'T' is not assignable to type 'U'.
                ~~~~
 !!! error TS2536: Type 'keyof U' cannot be used to index type 'T'.
     }
@@ -92,7 +107,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
-!!! error TS2322:   Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[K]'.
+!!! error TS2322:     Type 'T' is not assignable to type 'U'.
                ~~~~
 !!! error TS2536: Type 'K' cannot be used to index type 'T'.
     }
@@ -121,8 +137,11 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
-!!! error TS2322:   Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
-!!! error TS2322:     Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
+!!! error TS2322:     Type 'T[string]' is not assignable to type 'U[keyof T]'.
+!!! error TS2322:       Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
+!!! error TS2322:         Type 'T[string]' is not assignable to type 'U[keyof T]'.
+!!! error TS2322:           Type 'T' is not assignable to type 'U'.
     }
     
     function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
@@ -133,8 +152,11 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         y[k] = x[k];  // Error
         ~~~~
 !!! error TS2322: Type 'T[K]' is not assignable to type 'U[K] | undefined'.
-!!! error TS2322:   Type 'T[K]' is not assignable to type 'U[K]'.
-!!! error TS2322:     Type 'T' is not assignable to type 'U'.
+!!! error TS2322:   Type 'T[string]' is not assignable to type 'U[K] | undefined'.
+!!! error TS2322:     Type 'T[string]' is not assignable to type 'U[K]'.
+!!! error TS2322:       Type 'T[K]' is not assignable to type 'U[K]'.
+!!! error TS2322:         Type 'T[string]' is not assignable to type 'U[K]'.
+!!! error TS2322:           Type 'T' is not assignable to type 'U'.
     }
     
     function f20<T>(x: T, y: Readonly<T>, k: keyof T) {
@@ -247,7 +269,8 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         ~
 !!! error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
 !!! error TS2322:   Type 'T[P]' is not assignable to type 'U[P]'.
-!!! error TS2322:     Type 'T' is not assignable to type 'U'.
+!!! error TS2322:     Type 'T[string]' is not assignable to type 'U[P]'.
+!!! error TS2322:       Type 'T' is not assignable to type 'U'.
     }
     
     function f72<T, U extends T>(x: { [P in keyof T]: T[P] }, y: { [P in keyof U]: U[P] }) {
@@ -288,6 +311,7 @@ tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(167,5): error TS
         ~
 !!! error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in K]: U[P]; }'.
 !!! error TS2322:   Type 'T[P]' is not assignable to type 'U[P]'.
-!!! error TS2322:     Type 'T' is not assignable to type 'U'.
+!!! error TS2322:     Type 'T[string]' is not assignable to type 'U[P]'.
+!!! error TS2322:       Type 'T' is not assignable to type 'U'.
     }
     
\ No newline at end of file
diff --git a/tests/cases/compiler/indexedAccessTypeConstraints.ts b/tests/cases/compiler/indexedAccessTypeConstraints.ts
new file mode 100644
index 00000000000..c1c1bca198b
--- /dev/null
+++ b/tests/cases/compiler/indexedAccessTypeConstraints.ts
@@ -0,0 +1,36 @@
+// @strict: true
+
+// Repro from #14557
+
+interface IData<T> {
+    content: T;
+}
+
+type Data<T> = {
+    get: <K extends keyof T>(prop: K) => T[K];
+};
+
+class Parent<M> {
+    private data: Data<M>;
+    getData(): Data<M> {
+        return this.data;
+    }
+}
+
+export class Foo<C> extends Parent<IData<C>> {
+    getContent(): C {
+        return this.getData().get('content');
+    }
+}
+
+export class Bar<C, T extends IData<C>> extends Parent<T> {
+    getContent(): C {
+        return this.getData().get('content');
+    }
+}
+
+// Repro from #14557
+
+function foo<C, T extends { content: C }>(x: C, y: T['content']) {
+    x = y;
+}