diff --git a/tests/baselines/reference/inferTypes1.errors.txt b/tests/baselines/reference/inferTypes1.errors.txt
index d5b91a426e3..80edc31d37c 100644
--- a/tests/baselines/reference/inferTypes1.errors.txt
+++ b/tests/baselines/reference/inferTypes1.errors.txt
@@ -12,9 +12,10 @@ tests/cases/conformance/types/conditional/inferTypes1.ts(72,43): error TS2304: C
 tests/cases/conformance/types/conditional/inferTypes1.ts(72,43): error TS4081: Exported type alias 'T62' has or is using private name 'U'.
 tests/cases/conformance/types/conditional/inferTypes1.ts(78,44): error TS2344: Type 'U' does not satisfy the constraint 'string'.
   Type 'number' is not assignable to type 'string'.
+tests/cases/conformance/types/conditional/inferTypes1.ts(131,40): error TS2322: Type 'T' is not assignable to type 'string'.
 
 
-==== tests/cases/conformance/types/conditional/inferTypes1.ts (12 errors) ====
+==== tests/cases/conformance/types/conditional/inferTypes1.ts (13 errors) ====
     type Unpacked<T> =
         T extends (infer U)[] ? U :
         T extends (...args: any[]) => infer U ? U :
@@ -167,4 +168,11 @@ tests/cases/conformance/types/conditional/inferTypes1.ts(78,44): error TS2344: T
     type A2<T, U extends void> = [T, U];
     type B2<S> = S extends A2<infer T, infer U> ? [T, U] : never;
     type C2<S, U extends void> = S extends A2<infer T, U> ? [T, U] : never;
+    
+    // Repro from #21735
+    
+    type A<T> = T extends string ? { [P in T]: void; } : T;
+    type B<T> = string extends T ? { [P in T]: void; } : T;  // Error
+                                           ~
+!!! error TS2322: Type 'T' is not assignable to type 'string'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/inferTypes1.js b/tests/baselines/reference/inferTypes1.js
index 56bc71e5a71..21cada9c71b 100644
--- a/tests/baselines/reference/inferTypes1.js
+++ b/tests/baselines/reference/inferTypes1.js
@@ -125,6 +125,11 @@ type B1<S> = S extends A1<infer T, infer U> ? [T, U] : never;
 type A2<T, U extends void> = [T, U];
 type B2<S> = S extends A2<infer T, infer U> ? [T, U] : never;
 type C2<S, U extends void> = S extends A2<infer T, U> ? [T, U] : never;
+
+// Repro from #21735
+
+type A<T> = T extends string ? { [P in T]: void; } : T;
+type B<T> = string extends T ? { [P in T]: void; } : T;  // Error
 
 
 //// [inferTypes1.js]
diff --git a/tests/baselines/reference/inferTypes1.symbols b/tests/baselines/reference/inferTypes1.symbols
index 1e5468e2b8e..6e8a9670f29 100644
--- a/tests/baselines/reference/inferTypes1.symbols
+++ b/tests/baselines/reference/inferTypes1.symbols
@@ -551,3 +551,21 @@ type C2<S, U extends void> = S extends A2<infer T, U> ? [T, U] : never;
 >T : Symbol(T, Decl(inferTypes1.ts, 125, 47))
 >U : Symbol(U, Decl(inferTypes1.ts, 125, 10))
 
+// Repro from #21735
+
+type A<T> = T extends string ? { [P in T]: void; } : T;
+>A : Symbol(A, Decl(inferTypes1.ts, 125, 71))
+>T : Symbol(T, Decl(inferTypes1.ts, 129, 7))
+>T : Symbol(T, Decl(inferTypes1.ts, 129, 7))
+>P : Symbol(P, Decl(inferTypes1.ts, 129, 34))
+>T : Symbol(T, Decl(inferTypes1.ts, 129, 7))
+>T : Symbol(T, Decl(inferTypes1.ts, 129, 7))
+
+type B<T> = string extends T ? { [P in T]: void; } : T;  // Error
+>B : Symbol(B, Decl(inferTypes1.ts, 129, 55))
+>T : Symbol(T, Decl(inferTypes1.ts, 130, 7))
+>T : Symbol(T, Decl(inferTypes1.ts, 130, 7))
+>P : Symbol(P, Decl(inferTypes1.ts, 130, 34))
+>T : Symbol(T, Decl(inferTypes1.ts, 130, 7))
+>T : Symbol(T, Decl(inferTypes1.ts, 130, 7))
+
diff --git a/tests/baselines/reference/inferTypes1.types b/tests/baselines/reference/inferTypes1.types
index ca60ea57d0e..141a3d0aac6 100644
--- a/tests/baselines/reference/inferTypes1.types
+++ b/tests/baselines/reference/inferTypes1.types
@@ -558,3 +558,21 @@ type C2<S, U extends void> = S extends A2<infer T, U> ? [T, U] : never;
 >T : T
 >U : U
 
+// Repro from #21735
+
+type A<T> = T extends string ? { [P in T]: void; } : T;
+>A : A<T>
+>T : T
+>T : T
+>P : P
+>T : T
+>T : T
+
+type B<T> = string extends T ? { [P in T]: void; } : T;  // Error
+>B : B<T>
+>T : T
+>T : T
+>P : P
+>T : T
+>T : T
+