diff --git a/src/win/thread.c b/src/win/thread.c
index 89c53ada..3615101b 100644
--- a/src/win/thread.c
+++ b/src/win/thread.c
@@ -103,7 +103,7 @@ static UINT __stdcall uv__thread_start(void* arg) {
   uv__free(ctx_p);
 
   uv_once(&uv__current_thread_init_guard, uv__init_current_thread_key);
-  uv_key_set(&uv__current_thread_key, (void*) ctx.self);
+  uv_key_set(&uv__current_thread_key, ctx.self);
 
   ctx.entry(ctx.arg);
 
@@ -183,7 +183,18 @@ int uv_thread_create_ex(uv_thread_t* tid,
 
 uv_thread_t uv_thread_self(void) {
   uv_once(&uv__current_thread_init_guard, uv__init_current_thread_key);
-  return (uv_thread_t) uv_key_get(&uv__current_thread_key);
+  uv_thread_t key = uv_key_get(&uv__current_thread_key);
+  if (key == NULL) {
+      /* If the thread wasn't started by uv_thread_create (such as the main
+       * thread), we assign an id to it now. */
+      if (!DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
+                           GetCurrentProcess(), &key, 0,
+                           FALSE, DUPLICATE_SAME_ACCESS)) {
+          uv_fatal_error(GetLastError(), "DuplicateHandle");
+      }
+      uv_key_set(&uv__current_thread_key, key);
+  }
+  return key;
 }
 
 
diff --git a/test/test-thread-equal.c b/test/test-thread-equal.c
index 27c07ee2..f7bde71b 100644
--- a/test/test-thread-equal.c
+++ b/test/test-thread-equal.c
@@ -28,6 +28,9 @@ uv_thread_t subthreads[2];
 static void check_thread(void* arg) {
   uv_thread_t *thread_id = arg;
   uv_thread_t self_id = uv_thread_self();
+#ifdef _WIN32
+  ASSERT_NOT_NULL(self_id);
+#endif
   ASSERT(uv_thread_equal(&main_thread_id, &self_id) == 0);
   *thread_id = uv_thread_self();
 }
@@ -35,6 +38,9 @@ static void check_thread(void* arg) {
 TEST_IMPL(thread_equal) {
   uv_thread_t threads[2];
   main_thread_id = uv_thread_self();
+#ifdef _WIN32
+  ASSERT_NOT_NULL(main_thread_id);
+#endif
   ASSERT(0 != uv_thread_equal(&main_thread_id, &main_thread_id));
   ASSERT(0 == uv_thread_create(threads + 0, check_thread, subthreads + 0));
   ASSERT(0 == uv_thread_create(threads + 1, check_thread, subthreads + 1));