diff --git a/tests/baselines/reference/mappedTypeRelationships.errors.txt b/tests/baselines/reference/mappedTypeRelationships.errors.txt
new file mode 100644
index 00000000000..adafbc5f3a7
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeRelationships.errors.txt
@@ -0,0 +1,165 @@
+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'.
+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'.
+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(22,12): 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(27,12): 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]'.
+tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(36,5): error TS2322: Type 'T[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(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'.
+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'.
+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.
+tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(67,5): error TS2542: Index signature in type 'Readonly<U>' only permits reading.
+tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(71,5): error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
+tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(76,5): error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
+
+
+==== tests/cases/conformance/types/mapped/mappedTypeRelationships.ts (18 errors) ====
+    
+    function f1<T>(x: T, k: keyof T) {
+        return x[k];
+    }
+    
+    function f2<T, K extends keyof T>(x: T, k: K) {
+        return x[k];
+    }
+    
+    function f3<T, U extends T>(x: T, y: U, k: keyof T) {
+        x[k] = y[k];
+        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'.
+    }
+    
+    function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K) {
+        x[k] = y[k];
+        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'.
+    }
+    
+    function f5<T, U extends T>(x: T, y: U, k: keyof U) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2536: Type 'keyof U' cannot be used to index type 'T'.
+        y[k] = x[k];  // Error
+               ~~~~
+!!! error TS2536: Type 'keyof U' cannot be used to index type 'T'.
+    }
+    
+    function f6<T, U extends T, K extends keyof U>(x: T, y: U, k: K) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2536: Type 'K' cannot be used to index type 'T'.
+        y[k] = x[k];  // Error
+               ~~~~
+!!! error TS2536: Type 'K' cannot be used to index type 'T'.
+    }
+    
+    function f10<T>(x: T, y: Partial<T>, k: keyof T) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'T[keyof T]'.
+        y[k] = x[k];
+    }
+    
+    function f11<T, K extends keyof T>(x: T, y: Partial<T>, k: K) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2322: Type 'T[K] | undefined' is not assignable to type 'T[K]'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'T[K]'.
+        y[k] = x[k];
+    }
+    
+    function f12<T, U extends T>(x: T, y: Partial<U>, k: keyof T) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2322: Type 'U[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'T[keyof T]'.
+        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'.
+    }
+    
+    function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
+        x[k] = y[k];  // Error
+        ~~~~
+!!! error TS2322: Type 'U[K] | undefined' is not assignable to type 'T[K]'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'T[K]'.
+        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'.
+    }
+    
+    function f20<T>(x: T, y: Readonly<T>, k: keyof T) {
+        x[k] = y[k];
+        y[k] = x[k];  // Error
+        ~~~~
+!!! error TS2542: Index signature in type 'Readonly<T>' only permits reading.
+    }
+    
+    function f21<T, K extends keyof T>(x: T, y: Readonly<T>, k: K) {
+        x[k] = y[k];
+        y[k] = x[k];  // Error
+        ~~~~
+!!! error TS2542: Index signature in type 'Readonly<T>' only permits reading.
+    }
+    
+    function f22<T, U extends T>(x: T, y: Readonly<U>, k: keyof T) {
+        x[k] = y[k];
+        y[k] = x[k];  // Error
+        ~~~~
+!!! error TS2542: Index signature in type 'Readonly<U>' only permits reading.
+    }
+    
+    function f23<T, U extends T, K extends keyof T>(x: T, y: Readonly<U>, k: K) {
+        x[k] = y[k];
+        y[k] = x[k];  // Error
+        ~~~~
+!!! error TS2542: Index signature in type 'Readonly<U>' only permits reading.
+    }
+    
+    function f30<T>(x: T, y: Partial<T>) {
+        x = y;  // Error
+        ~
+!!! error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
+        y = x;
+    }
+    
+    function f31<T>(x: T, y: Partial<T>) {
+        x = y;  // Error
+        ~
+!!! error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
+        y = x;
+    }
+    
+    function f40<T>(x: T, y: Readonly<T>) {
+        x = y;
+        y = x;
+    }
+    
+    function f41<T>(x: T, y: Readonly<T>) {
+        x = y;
+        y = x;
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/mappedTypeRelationships.js b/tests/baselines/reference/mappedTypeRelationships.js
new file mode 100644
index 00000000000..fcad6973ab7
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeRelationships.js
@@ -0,0 +1,182 @@
+//// [mappedTypeRelationships.ts]
+
+function f1<T>(x: T, k: keyof T) {
+    return x[k];
+}
+
+function f2<T, K extends keyof T>(x: T, k: K) {
+    return x[k];
+}
+
+function f3<T, U extends T>(x: T, y: U, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f5<T, U extends T>(x: T, y: U, k: keyof U) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f6<T, U extends T, K extends keyof U>(x: T, y: U, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f10<T>(x: T, y: Partial<T>, k: keyof T) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];
+}
+
+function f11<T, K extends keyof T>(x: T, y: Partial<T>, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];
+}
+
+function f12<T, U extends T>(x: T, y: Partial<U>, k: keyof T) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f20<T>(x: T, y: Readonly<T>, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f21<T, K extends keyof T>(x: T, y: Readonly<T>, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f22<T, U extends T>(x: T, y: Readonly<U>, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f23<T, U extends T, K extends keyof T>(x: T, y: Readonly<U>, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f30<T>(x: T, y: Partial<T>) {
+    x = y;  // Error
+    y = x;
+}
+
+function f31<T>(x: T, y: Partial<T>) {
+    x = y;  // Error
+    y = x;
+}
+
+function f40<T>(x: T, y: Readonly<T>) {
+    x = y;
+    y = x;
+}
+
+function f41<T>(x: T, y: Readonly<T>) {
+    x = y;
+    y = x;
+}
+
+//// [mappedTypeRelationships.js]
+function f1(x, k) {
+    return x[k];
+}
+function f2(x, k) {
+    return x[k];
+}
+function f3(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f4(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f5(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k]; // Error
+}
+function f6(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k]; // Error
+}
+function f10(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k];
+}
+function f11(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k];
+}
+function f12(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k]; // Error
+}
+function f13(x, y, k) {
+    x[k] = y[k]; // Error
+    y[k] = x[k]; // Error
+}
+function f20(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f21(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f22(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f23(x, y, k) {
+    x[k] = y[k];
+    y[k] = x[k]; // Error
+}
+function f30(x, y) {
+    x = y; // Error
+    y = x;
+}
+function f31(x, y) {
+    x = y; // Error
+    y = x;
+}
+function f40(x, y) {
+    x = y;
+    y = x;
+}
+function f41(x, y) {
+    x = y;
+    y = x;
+}
+
+
+//// [mappedTypeRelationships.d.ts]
+declare function f1<T>(x: T, k: keyof T): T[keyof T];
+declare function f2<T, K extends keyof T>(x: T, k: K): T[K];
+declare function f3<T, U extends T>(x: T, y: U, k: keyof T): void;
+declare function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K): void;
+declare function f5<T, U extends T>(x: T, y: U, k: keyof U): void;
+declare function f6<T, U extends T, K extends keyof U>(x: T, y: U, k: K): void;
+declare function f10<T>(x: T, y: Partial<T>, k: keyof T): void;
+declare function f11<T, K extends keyof T>(x: T, y: Partial<T>, k: K): void;
+declare function f12<T, U extends T>(x: T, y: Partial<U>, k: keyof T): void;
+declare function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K): void;
+declare function f20<T>(x: T, y: Readonly<T>, k: keyof T): void;
+declare function f21<T, K extends keyof T>(x: T, y: Readonly<T>, k: K): void;
+declare function f22<T, U extends T>(x: T, y: Readonly<U>, k: keyof T): void;
+declare function f23<T, U extends T, K extends keyof T>(x: T, y: Readonly<U>, k: K): void;
+declare function f30<T>(x: T, y: Partial<T>): void;
+declare function f31<T>(x: T, y: Partial<T>): void;
+declare function f40<T>(x: T, y: Readonly<T>): void;
+declare function f41<T>(x: T, y: Readonly<T>): void;
diff --git a/tests/cases/conformance/types/mapped/mappedTypeRelationships.ts b/tests/cases/conformance/types/mapped/mappedTypeRelationships.ts
new file mode 100644
index 00000000000..7bc1c1a1670
--- /dev/null
+++ b/tests/cases/conformance/types/mapped/mappedTypeRelationships.ts
@@ -0,0 +1,90 @@
+// @strictNullChecks: true
+// @declaration: true
+
+function f1<T>(x: T, k: keyof T) {
+    return x[k];
+}
+
+function f2<T, K extends keyof T>(x: T, k: K) {
+    return x[k];
+}
+
+function f3<T, U extends T>(x: T, y: U, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f5<T, U extends T>(x: T, y: U, k: keyof U) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f6<T, U extends T, K extends keyof U>(x: T, y: U, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f10<T>(x: T, y: Partial<T>, k: keyof T) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];
+}
+
+function f11<T, K extends keyof T>(x: T, y: Partial<T>, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];
+}
+
+function f12<T, U extends T>(x: T, y: Partial<U>, k: keyof T) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
+    x[k] = y[k];  // Error
+    y[k] = x[k];  // Error
+}
+
+function f20<T>(x: T, y: Readonly<T>, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f21<T, K extends keyof T>(x: T, y: Readonly<T>, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f22<T, U extends T>(x: T, y: Readonly<U>, k: keyof T) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f23<T, U extends T, K extends keyof T>(x: T, y: Readonly<U>, k: K) {
+    x[k] = y[k];
+    y[k] = x[k];  // Error
+}
+
+function f30<T>(x: T, y: Partial<T>) {
+    x = y;  // Error
+    y = x;
+}
+
+function f31<T>(x: T, y: Partial<T>) {
+    x = y;  // Error
+    y = x;
+}
+
+function f40<T>(x: T, y: Readonly<T>) {
+    x = y;
+    y = x;
+}
+
+function f41<T>(x: T, y: Readonly<T>) {
+    x = y;
+    y = x;
+}
\ No newline at end of file