diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols b/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
index 36fb8d2989b..0e97ef793fb 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.symbols
@@ -268,3 +268,34 @@ function f20<T, U>(k1: keyof (T | U), k2: keyof (T & U), o1: T | U, o2: T & U) {
 >k2 : Symbol(k2, Decl(keyofAndIndexedAccessErrors.ts, 69, 37))
 >k1 : Symbol(k1, Decl(keyofAndIndexedAccessErrors.ts, 69, 19))
 }
+
+// Repro from #17166
+function f3<T, K extends keyof T>(obj: T, k: K, value: T[K]): void {
+>f3 : Symbol(f3, Decl(keyofAndIndexedAccessErrors.ts, 78, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 81, 12))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 81, 14))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 81, 12))
+>obj : Symbol(obj, Decl(keyofAndIndexedAccessErrors.ts, 81, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 81, 12))
+>k : Symbol(k, Decl(keyofAndIndexedAccessErrors.ts, 81, 41))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 81, 14))
+>value : Symbol(value, Decl(keyofAndIndexedAccessErrors.ts, 81, 47))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 81, 12))
+>K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 81, 14))
+
+    for (let key in obj) {
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 82, 12))
+>obj : Symbol(obj, Decl(keyofAndIndexedAccessErrors.ts, 81, 34))
+
+        k = key // error, keyof T =/=> K
+>k : Symbol(k, Decl(keyofAndIndexedAccessErrors.ts, 81, 41))
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 82, 12))
+
+        value = obj[key]; // error, T[keyof T] =/=> T[K]
+>value : Symbol(value, Decl(keyofAndIndexedAccessErrors.ts, 81, 47))
+>obj : Symbol(obj, Decl(keyofAndIndexedAccessErrors.ts, 81, 34))
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 82, 12))
+    }
+}
+
+
diff --git a/tests/baselines/reference/keyofAndIndexedAccessErrors.types b/tests/baselines/reference/keyofAndIndexedAccessErrors.types
index 4d2e25641d3..f5cc7c093d9 100644
--- a/tests/baselines/reference/keyofAndIndexedAccessErrors.types
+++ b/tests/baselines/reference/keyofAndIndexedAccessErrors.types
@@ -299,3 +299,37 @@ function f20<T, U>(k1: keyof (T | U), k2: keyof (T & U), o1: T | U, o2: T & U) {
 >k2 : keyof (T & U)
 >k1 : keyof (T | U)
 }
+
+// Repro from #17166
+function f3<T, K extends keyof T>(obj: T, k: K, value: T[K]): void {
+>f3 : <T, K extends keyof T>(obj: T, k: K, value: T[K]) => void
+>T : T
+>K : K
+>T : T
+>obj : T
+>T : T
+>k : K
+>K : K
+>value : T[K]
+>T : T
+>K : K
+
+    for (let key in obj) {
+>key : keyof T
+>obj : T
+
+        k = key // error, keyof T =/=> K
+>k = key : keyof T
+>k : K
+>key : keyof T
+
+        value = obj[key]; // error, T[keyof T] =/=> T[K]
+>value = obj[key] : T[keyof T]
+>value : T[K]
+>obj[key] : T[keyof T]
+>obj : T
+>key : keyof T
+    }
+}
+
+
diff --git a/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.symbols b/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.symbols
new file mode 100644
index 00000000000..3ada1e3f3d1
--- /dev/null
+++ b/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.symbols
@@ -0,0 +1,145 @@
+=== tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts ===
+// test for #15371
+function f<T extends object, P extends keyof T>(s: string, tp: T[P]): void {
+>f : Symbol(f, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 0, 0))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 28))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 48))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 58))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 28))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 58))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 1, 48))
+}
+function g<T extends null, P extends keyof T>(s: string, tp: T[P]): void {
+>g : Symbol(g, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 3, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 26))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 46))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 56))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 26))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 56))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 4, 46))
+}
+function h<T extends undefined, P extends keyof T>(s: string, tp: T[P]): void {
+>h : Symbol(h, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 6, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 31))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 51))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 61))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 31))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 61))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 7, 51))
+}
+function i<T extends void, P extends keyof T>(s: string, tp: T[P]): void {
+>i : Symbol(i, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 9, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 26))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 46))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 56))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 26))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 56))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 10, 46))
+}
+function j<T extends never, P extends keyof T>(s: string, tp: T[P]): void {
+>j : Symbol(j, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 12, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 27))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 47))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 57))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 27))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 57))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 13, 47))
+}
+function k<T extends number, P extends keyof T>(s: string, tp: T[P]): void {
+>k : Symbol(k, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 15, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 28))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 48))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 58))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 28))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 58))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 16, 48))
+}
+function o<T extends string, P extends keyof T>(s: string, tp: T[P]): void {
+>o : Symbol(o, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 18, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 28))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 48))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 58))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 28))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 58))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 19, 48))
+}
+function l<T extends {}, P extends keyof T>(s: string, tp: T[P]): void {
+>l : Symbol(l, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 21, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 24))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 44))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 54))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 24))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 54))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 22, 44))
+}
+function m<T extends { a: number }, P extends keyof T>(s: string, tp: T[P]): void {
+>m : Symbol(m, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 24, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 11))
+>a : Symbol(a, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 22))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 35))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 55))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 65))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 35))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 65))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 25, 55))
+}
+function n<T extends { [s: string]: number }, P extends keyof T>(s: string, tp: T[P]): void {
+>n : Symbol(n, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 27, 1))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 24))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 45))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 11))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 65))
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 75))
+>T : Symbol(T, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 11))
+>P : Symbol(P, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 45))
+
+    tp = s;
+>tp : Symbol(tp, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 75))
+>s : Symbol(s, Decl(nonPrimitiveConstraintOfIndexAccessType.ts, 28, 65))
+}
+
diff --git a/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.types b/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.types
new file mode 100644
index 00000000000..d5e8560d7cf
--- /dev/null
+++ b/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.types
@@ -0,0 +1,156 @@
+=== tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts ===
+// test for #15371
+function f<T extends object, P extends keyof T>(s: string, tp: T[P]): void {
+>f : <T extends object, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function g<T extends null, P extends keyof T>(s: string, tp: T[P]): void {
+>g : <T extends null, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>null : null
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function h<T extends undefined, P extends keyof T>(s: string, tp: T[P]): void {
+>h : <T extends undefined, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function i<T extends void, P extends keyof T>(s: string, tp: T[P]): void {
+>i : <T extends void, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function j<T extends never, P extends keyof T>(s: string, tp: T[P]): void {
+>j : <T extends never, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function k<T extends number, P extends keyof T>(s: string, tp: T[P]): void {
+>k : <T extends number, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function o<T extends string, P extends keyof T>(s: string, tp: T[P]): void {
+>o : <T extends string, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function l<T extends {}, P extends keyof T>(s: string, tp: T[P]): void {
+>l : <T extends {}, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function m<T extends { a: number }, P extends keyof T>(s: string, tp: T[P]): void {
+>m : <T extends { a: number; }, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>a : number
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+function n<T extends { [s: string]: number }, P extends keyof T>(s: string, tp: T[P]): void {
+>n : <T extends { [s: string]: number; }, P extends keyof T>(s: string, tp: T[P]) => void
+>T : T
+>s : string
+>P : P
+>T : T
+>s : string
+>tp : T[P]
+>T : T
+>P : P
+
+    tp = s;
+>tp = s : string
+>tp : T[P]
+>s : string
+}
+