--- a/widget/windows/nsSound.cpp
+++ b/widget/windows/nsSound.cpp
@@ -119,20 +119,19 @@ nsSound::nsSound()
 nsSound::~nsSound()
 {
   NS_ASSERTION(!mPlayerThread, "player thread is not null but should be");
   PurgeLastSound();
 }
 
 void nsSound::ShutdownOldPlayerThread()
 {
-  if (mPlayerThread) {
-    mPlayerThread->Shutdown();
-    mPlayerThread = nullptr;
-  }
+  nsCOMPtr<nsIThread> playerThread(mPlayerThread.forget());
+  if (playerThread)
+    playerThread->Shutdown();
 }
 
 void nsSound::PurgeLastSound() 
 {
   if (mLastSound) {
     // Halt any currently playing sound.
     ::PlaySound(nullptr, nullptr, SND_PURGE);