--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -2800,49 +2800,52 @@ MediaDecoderStateMachine::IsVideoDecodin
 }
 
 bool MediaDecoderStateMachine::IsPlaying() const
 {
   MOZ_ASSERT(OnTaskQueue());
   return mMediaSink->IsPlaying();
 }
 
+void MediaDecoderStateMachine::SetMediaNotSeekable()
+{
+  mMediaSeekable = false;
+}
+
 nsresult MediaDecoderStateMachine::Init(MediaDecoder* aDecoder)
 {
   MOZ_ASSERT(NS_IsMainThread());
 
   // Dispatch initialization that needs to happen on that task queue.
   nsCOMPtr<nsIRunnable> r = NewRunnableMethod<RefPtr<MediaDecoder>>(
     this, &MediaDecoderStateMachine::InitializationTask, aDecoder);
   mTaskQueue->Dispatch(r.forget());
 
   mAudioQueueListener = AudioQueue().PopEvent().Connect(
     mTaskQueue, this, &MediaDecoderStateMachine::OnAudioPopped);
   mVideoQueueListener = VideoQueue().PopEvent().Connect(
     mTaskQueue, this, &MediaDecoderStateMachine::OnVideoPopped);
 
   mMetadataManager.Connect(mReader->TimedMetadataEvent(), OwnerThread());
 
-  RefPtr<MediaDecoderStateMachine> self = this;
   mOnMediaNotSeekable = mReader->OnMediaNotSeekable().Connect(
-    OwnerThread(), [self] () {
-      self->mMediaSeekable = false;
-    });
+    OwnerThread(), this, &MediaDecoderStateMachine::SetMediaNotSeekable);
 
   mMediaSink = CreateMediaSink(mAudioCaptured);
 
   aDecoder->RequestCDMProxy()->Then(
     OwnerThread(), __func__, this,
     &MediaDecoderStateMachine::OnCDMProxyReady,
     &MediaDecoderStateMachine::OnCDMProxyNotReady)
   ->Track(mCDMProxyPromise);
 
   nsresult rv = mReader->Init();
   NS_ENSURE_SUCCESS(rv, rv);
 
+  RefPtr<MediaDecoderStateMachine> self = this;
   OwnerThread()->Dispatch(NS_NewRunnableFunction([self] () {
     MOZ_ASSERT(!self->mStateObj);
     auto s = new DecodeMetadataState(self);
     self->mStateObj.reset(s);
     s->Enter();
   }));
 
   return NS_OK;

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -292,16 +292,19 @@ private:
 
   // True if shutdown process has begun.
   bool IsShutdown() const;
 
   // Returns true if we're currently playing. The decoder monitor must
   // be held.
   bool IsPlaying() const;
 
+  // Sets mMediaSeekable to false.
+  void SetMediaNotSeekable();
+
   // Resets all states related to decoding and aborts all pending requests
   // to the decoders.
   void ResetDecode(TrackSet aTracks = TrackSet(TrackInfo::kAudioTrack,
                                                TrackInfo::kVideoTrack));
 
 protected:
   virtual ~MediaDecoderStateMachine();