diff --git a/src/unix/loop-watcher.c b/src/unix/loop-watcher.c
index 9d1414b8..a07569e4 100644
--- a/src/unix/loop-watcher.c
+++ b/src/unix/loop-watcher.c
@@ -31,6 +31,8 @@
                                                                               \
   int uv_##name##_start(uv_##name##_t* handle, uv_##name##_cb cb) {           \
     if (uv__is_active(handle)) return 0;                                      \
+    if (cb == NULL)                                                           \
+      return uv__set_artificial_error(handle->loop, UV_EINVAL);               \
     ngx_queue_insert_head(&handle->loop->name##_handles, &handle->queue);     \
     handle->name##_cb = cb;                                                   \
     uv__handle_start(handle);                                                 \
@@ -49,7 +51,7 @@
     ngx_queue_t* q;                                                           \
     ngx_queue_foreach(q, &loop->name##_handles) {                             \
       h = ngx_queue_data(q, uv_##name##_t, queue);                            \
-      if (h->name##_cb) h->name##_cb(h, 0);                                   \
+      h->name##_cb(h, 0);                                                     \
     }                                                                         \
   }                                                                           \
                                                                               \
diff --git a/src/win/loop-watcher.c b/src/win/loop-watcher.c
index 9fff631c..65080ff6 100644
--- a/src/win/loop-watcher.c
+++ b/src/win/loop-watcher.c
@@ -52,6 +52,9 @@ void uv_loop_watcher_endgame(uv_loop_t* loop, uv_handle_t* handle) {
     if (handle->flags & UV_HANDLE_ACTIVE)                                     \
       return 0;                                                               \
                                                                               \
+    if (cb == NULL)                                                           \
+      return uv__set_artificial_error(handle->loop, UV_EINVAL);               \
+                                                                              \
     old_head = loop->name##_handles;                                          \
                                                                               \
     handle->name##_next = old_head;                                           \
diff --git a/test/test-ref.c b/test/test-ref.c
index bc0030d3..027af16f 100644
--- a/test/test-ref.c
+++ b/test/test-ref.c
@@ -58,6 +58,11 @@ static void fail_cb(void) {
 }
 
 
+static void fail_cb2() {
+  ASSERT(0 && "fail_cb2 should not have been called");
+}
+
+
 static void req_cb(uv_handle_t* req, int status) {
   req_cb_called++;
 }
@@ -104,7 +109,7 @@ TEST_IMPL(ref) {
 TEST_IMPL(idle_ref) {
   uv_idle_t h;
   uv_idle_init(uv_default_loop(), &h);
-  uv_idle_start(&h, NULL);
+  uv_idle_start(&h, fail_cb2);
   uv_unref((uv_handle_t*)&h);
   uv_run(uv_default_loop());
   do_close(&h);
@@ -127,7 +132,7 @@ TEST_IMPL(async_ref) {
 TEST_IMPL(prepare_ref) {
   uv_prepare_t h;
   uv_prepare_init(uv_default_loop(), &h);
-  uv_prepare_start(&h, NULL);
+  uv_prepare_start(&h, fail_cb2);
   uv_unref((uv_handle_t*)&h);
   uv_run(uv_default_loop());
   do_close(&h);
@@ -139,7 +144,7 @@ TEST_IMPL(prepare_ref) {
 TEST_IMPL(check_ref) {
   uv_check_t h;
   uv_check_init(uv_default_loop(), &h);
-  uv_check_start(&h, NULL);
+  uv_check_start(&h, fail_cb2);
   uv_unref((uv_handle_t*)&h);
   uv_run(uv_default_loop());
   do_close(&h);