diff --git a/stdlib/public/runtime/ThreadLocalStorage.h b/stdlib/public/runtime/ThreadLocalStorage.h
index c3a50a24fc1..c15db88092b 100644
--- a/stdlib/public/runtime/ThreadLocalStorage.h
+++ b/stdlib/public/runtime/ThreadLocalStorage.h
@@ -90,7 +90,7 @@ static_assert(std::is_same<__swift_thread_key_t, DWORD>::value,
 
 #  define SWIFT_THREAD_KEY_CREATE _stdlib_thread_key_create
 #  define SWIFT_THREAD_GETSPECIFIC FlsGetValue
-#  define SWIFT_THREAD_SETSPECIFIC(key, value) (FlsSetValue(key, value) == TRUE)
+#  define SWIFT_THREAD_SETSPECIFIC(key, value) (FlsSetValue(key, value) == FALSE)
 
 # else
 // Otherwise use the pthread API.
diff --git a/stdlib/public/stubs/ThreadLocalStorage.cpp b/stdlib/public/stubs/ThreadLocalStorage.cpp
index 3da65bd1374..219a13c652c 100644
--- a/stdlib/public/stubs/ThreadLocalStorage.cpp
+++ b/stdlib/public/stubs/ThreadLocalStorage.cpp
@@ -43,7 +43,9 @@ static inline int
 _stdlib_thread_key_create(__swift_thread_key_t * _Nonnull key,
                           __swift_thread_key_destructor _Nullable destructor) {
   *key = FlsAlloc(destroyTLS_CCAdjustmentThunk);
-  return *key != FLS_OUT_OF_INDEXES;
+  if (*key == FLS_OUT_OF_INDEXES)
+    return GetLastError();
+  return 0;
 }
 
 #endif