diff --git a/dom/media/AudioSink.cpp b/dom/media/AudioSink.cpp
index b1465d20ff31..7e4f2bc2d831 100644
--- a/dom/media/AudioSink.cpp
+++ b/dom/media/AudioSink.cpp
@@ -25,6 +25,38 @@ extern PRLogModuleInfo* gMediaDecoderLog;
 #define SINK_LOG_V(msg, ...)
 #endif
 
+AudioSink::OnAudioEndTimeUpdateTask::OnAudioEndTimeUpdateTask(
+                                     MediaDecoderStateMachine* aStateMachine)
+  : mMutex("OnAudioEndTimeUpdateTask")
+  , mEndTime(0)
+  , mStateMachine(aStateMachine)
+{
+}
+
+NS_IMETHODIMP
+AudioSink::OnAudioEndTimeUpdateTask::Run() {
+  MutexAutoLock lock(mMutex);
+  if (mStateMachine) {
+    mStateMachine->OnAudioEndTimeUpdate(mEndTime);
+  }
+  return NS_OK;
+}
+
+void
+AudioSink::OnAudioEndTimeUpdateTask::Dispatch(int64_t aEndTime) {
+  MutexAutoLock lock(mMutex);
+  if (mStateMachine) {
+    mEndTime = aEndTime;
+    mStateMachine->TaskQueue()->Dispatch(this);
+  }
+}
+
+void
+AudioSink::OnAudioEndTimeUpdateTask::Cancel() {
+  MutexAutoLock lock(mMutex);
+  mStateMachine = nullptr;
+}
+
 // The amount of audio frames that is used to fuzz rounding errors.
 static const int64_t AUDIO_FUZZ_FRAMES = 1;
 
@@ -46,6 +78,7 @@ AudioSink::AudioSink(MediaDecoderStateMachine* aStateMachine,
   , mPlaying(true)
 {
   NS_ASSERTION(mStartTime != -1, "Should have audio start time by now");
+  mOnAudioEndTimeUpdateTask = new OnAudioEndTimeUpdateTask(aStateMachine);
 }
 
 nsresult
@@ -108,6 +141,7 @@ AudioSink::PrepareToShutdown()
 void
 AudioSink::Shutdown()
 {
+  mOnAudioEndTimeUpdateTask->Cancel();
   mThread->Shutdown();
   mThread = nullptr;
   MOZ_ASSERT(!mAudioStream);
@@ -202,7 +236,7 @@ AudioSink::AudioLoop()
     }
     int64_t endTime = GetEndTime();
     if (endTime != -1) {
-      mStateMachine->DispatchOnAudioEndTimeUpdate(endTime);
+      mOnAudioEndTimeUpdateTask->Dispatch(endTime);
     }
   }
   ReentrantMonitorAutoEnter mon(GetReentrantMonitor());
diff --git a/dom/media/AudioSink.h b/dom/media/AudioSink.h
index 8863bcaa92fc..3b8877c0a75c 100644
--- a/dom/media/AudioSink.h
+++ b/dom/media/AudioSink.h
@@ -139,6 +139,23 @@ private:
   bool mSetPreservesPitch;
 
   bool mPlaying;
+
+  class OnAudioEndTimeUpdateTask : public nsRunnable {
+  public:
+    explicit OnAudioEndTimeUpdateTask(MediaDecoderStateMachine* aStateMachine);
+
+    NS_IMETHOD Run() override;
+
+    void Dispatch(int64_t aEndTime);
+    void Cancel();
+
+  private:
+    Mutex mMutex;
+    int64_t mEndTime;
+    nsRefPtr<MediaDecoderStateMachine> mStateMachine;
+  };
+
+  nsRefPtr<OnAudioEndTimeUpdateTask> mOnAudioEndTimeUpdateTask;
 };
 
 } // namespace mozilla
diff --git a/dom/media/MediaDecoderStateMachine.h b/dom/media/MediaDecoderStateMachine.h
index 9e21e6ebea64..e486c2673412 100644
--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -713,16 +713,9 @@ protected:
   // Can only be called on the state machine thread.
   void SetPlayStartTime(const TimeStamp& aTimeStamp);
 
-private:
+public:
   // Update mAudioEndTime.
   void OnAudioEndTimeUpdate(int64_t aAudioEndTime);
-public:
-  void DispatchOnAudioEndTimeUpdate(int64_t aAudioEndTime)
-  {
-    RefPtr<nsRunnable> r =
-      NS_NewRunnableMethodWithArg<int64_t>(this, &MediaDecoderStateMachine::OnAudioEndTimeUpdate, aAudioEndTime);
-    TaskQueue()->Dispatch(r.forget());
-  }
 
 private:
   // Update mDecoder's playback offset.