--- a/xpcom/threads/SynchronizedEventQueue.cpp
+++ b/xpcom/threads/SynchronizedEventQueue.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "SynchronizedEventQueue.h"
+#include "nsIThreadInternal.h"
 
 using namespace mozilla;
 
 void
 SynchronizedEventQueue::AddObserver(nsIThreadObserver* aObserver)
 {
   MOZ_ASSERT(aObserver);
   MOZ_ASSERT(!mEventObservers.Contains(aObserver));