diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt b/tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt
index cba7ab52469..68669463d95 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt
@@ -66,9 +66,10 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(123,5): error
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(140,5): error TS2322: Type '42' is not assignable to type 'T[K]'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(141,5): error TS2322: Type '"hello"' is not assignable to type 'T[K]'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(142,5): error TS2322: Type 'number[]' is not assignable to type 'T[K]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(158,9): error TS2322: Type '"hello"' is not assignable to type 'Record<keyof T, string>[K]'.
 
 
-==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (41 errors) ====
+==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (42 errors) ====
     class Shape {
         name: string;
         width: number;
@@ -321,4 +322,22 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(142,5): error
         ~~~~
 !!! error TS2322: Type 'number[]' is not assignable to type 'T[K]'.
     }
+    
+    // Repro from #28839
+    
+    function f30<T, K extends keyof T>() {
+        let x: Partial<Record<keyof T, string>>[K] = "hello";
+    }
+    
+    // We simplify indexed accesses applied to mapped types up to five levels deep
+    
+    function f31<T, K extends keyof T>() {
+        let x: Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K] = "hello";
+    }
+    
+    function f32<T, K extends keyof T>() {
+        let x: Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K] = "hello";
+            ~
+!!! error TS2322: Type '"hello"' is not assignable to type 'Record<keyof T, string>[K]'.
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.js b/tests/baselines/reference/keyofAndIndexedAccessErrors.js
index 88a1b74f14d..0cf77e79ba6 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.js
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.js
@@ -142,6 +142,22 @@ function test1<T extends Record<string, any>, K extends keyof T>(t: T, k: K) {
     t[k] = "hello";  // Error
     t[k] = [10, 20];  // Error
 }
+
+// Repro from #28839
+
+function f30<T, K extends keyof T>() {
+    let x: Partial<Record<keyof T, string>>[K] = "hello";
+}
+
+// We simplify indexed accesses applied to mapped types up to five levels deep
+
+function f31<T, K extends keyof T>() {
+    let x: Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K] = "hello";
+}
+
+function f32<T, K extends keyof T>() {
+    let x: Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K] = "hello";
+}
 
 
 //// [keyofAndIndexedAccessErrors.js]
@@ -215,3 +231,14 @@ function test1(t, k) {
     t[k] = "hello"; // Error
     t[k] = [10, 20]; // Error
 }
+// Repro from #28839
+function f30() {
+    var x = "hello";
+}
+// We simplify indexed accesses applied to mapped types up to five levels deep
+function f31() {
+    var x = "hello";
+}
+function f32() {
+    var x = "hello";
+}
diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols b/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
index df1707849cb..3f32679a813 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
@@ -486,3 +486,56 @@ function test1<T extends Record<string, any>, K extends keyof T>(t: T, k: K) {
 >k : Symbol(k, Decl(keyofAndIndexedAccessErrors.ts, 138, 70))
 }
 
+// Repro from #28839
+
+function f30<T, K extends keyof T>() {
+>f30 : Symbol(f30, Decl(keyofAndIndexedAccessErrors.ts, 142, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 146, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 146, 15))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 146, 13))
+
+    let x: Partial<Record<keyof T, string>>[K] = "hello";
+>x : Symbol(x, Decl(keyofAndIndexedAccessErrors.ts, 147, 7))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 146, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 146, 15))
+}
+
+// We simplify indexed accesses applied to mapped types up to five levels deep
+
+function f31<T, K extends keyof T>() {
+>f31 : Symbol(f31, Decl(keyofAndIndexedAccessErrors.ts, 148, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 152, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 152, 15))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 152, 13))
+
+    let x: Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K] = "hello";
+>x : Symbol(x, Decl(keyofAndIndexedAccessErrors.ts, 153, 7))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 152, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 152, 15))
+}
+
+function f32<T, K extends keyof T>() {
+>f32 : Symbol(f32, Decl(keyofAndIndexedAccessErrors.ts, 154, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 156, 15))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 13))
+
+    let x: Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K] = "hello";
+>x : Symbol(x, Decl(keyofAndIndexedAccessErrors.ts, 157, 7))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 13))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 156, 15))
+}
+
diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.types b/tests/baselines/reference/keyofAndIndexedAccessErrors.types
index 68dc361c99e..b9d17df0341 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.types
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.types
@@ -465,3 +465,31 @@ function test1<T extends Record<string, any>, K extends keyof T>(t: T, k: K) {
 >20 : 20
 }
 
+// Repro from #28839
+
+function f30<T, K extends keyof T>() {
+>f30 : <T, K extends keyof T>() => void
+
+    let x: Partial<Record<keyof T, string>>[K] = "hello";
+>x : Partial<Record<keyof T, string>>[K]
+>"hello" : "hello"
+}
+
+// We simplify indexed accesses applied to mapped types up to five levels deep
+
+function f31<T, K extends keyof T>() {
+>f31 : <T, K extends keyof T>() => void
+
+    let x: Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K] = "hello";
+>x : Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>[K]
+>"hello" : "hello"
+}
+
+function f32<T, K extends keyof T>() {
+>f32 : <T, K extends keyof T>() => void
+
+    let x: Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K] = "hello";
+>x : Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>[K]
+>"hello" : "hello"
+}
+