--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -2080,17 +2080,17 @@ DecodingState::Enter()
   if (!mMaster->mIsVisible &&
       !mMaster->mVideoDecodeSuspendTimer.IsScheduled() &&
       !mMaster->mVideoDecodeSuspended) {
     // If we are not visible and the timer is not schedule, it means the timer
     // has timed out and we should suspend video decoding now if necessary.
     HandleVideoSuspendTimeout();
   }
 
-  if (mMaster->CheckIfDecodeComplete()) {
+  if (!mMaster->IsVideoDecoding() && !mMaster->IsAudioDecoding()) {
     SetState<CompletedState>();
     return;
   }
 
   mOnAudioPopped = AudioQueue().PopEvent().Connect(
     OwnerThread(), [this] () {
     if (mMaster->IsAudioDecoding() && !mMaster->HaveEnoughDecodedAudio()) {
       EnsureAudioDecodeTaskQueued();
@@ -2693,27 +2693,16 @@ MediaDecoderStateMachine::IsAudioDecodin
 
 bool
 MediaDecoderStateMachine::IsVideoDecoding()
 {
   MOZ_ASSERT(OnTaskQueue());
   return HasVideo() && !VideoQueue().IsFinished();
 }
 
-bool
-MediaDecoderStateMachine::CheckIfDecodeComplete()
-{
-  MOZ_ASSERT(OnTaskQueue());
-  // DecodeComplete is possible only after decoding first frames.
-  MOZ_ASSERT(mSentFirstFrameLoadedEvent);
-  MOZ_ASSERT(mState == DECODER_STATE_DECODING ||
-             mState == DECODER_STATE_BUFFERING);
-  return !IsVideoDecoding() && !IsAudioDecoding();
-}
-
 bool MediaDecoderStateMachine::IsPlaying() const
 {
   MOZ_ASSERT(OnTaskQueue());
   return mMediaSink->IsPlaying();
 }
 
 nsresult MediaDecoderStateMachine::Init(MediaDecoder* aDecoder)
 {

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -438,19 +438,16 @@ protected:
   // which has been pushed to the audio hardware for playback. Note that after
   // calling this, the audio hardware may play some of the audio pushed to
   // hardware, so this can only be used as a upper bound. The decoder monitor
   // must be held when calling this. Called on the decode thread.
   int64_t GetDecodedAudioDuration();
 
   void FinishDecodeFirstFrame();
 
-  // Queries our state to see whether the decode has finished for all streams.
-  bool CheckIfDecodeComplete();
-
   // Performs one "cycle" of the state machine.
   void RunStateMachine();
 
   bool IsStateMachineScheduled() const;
 
   // These return true if the respective stream's decode has not yet reached
   // the end of stream.
   bool IsAudioDecoding();