--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -1485,20 +1485,20 @@ RefPtr<MediaDecoderReader::SeekPromise>
 MediaFormatReader::Seek(SeekTarget aTarget, int64_t aUnused)
 {
   MOZ_ASSERT(OnTaskQueue());
 
   LOG("aTarget=(%lld)", aTarget.GetTime().ToMicroseconds());
 
   MOZ_DIAGNOSTIC_ASSERT(mSeekPromise.IsEmpty());
   MOZ_DIAGNOSTIC_ASSERT(!mVideo.HasPromise());
-  MOZ_DIAGNOSTIC_ASSERT(!mAudio.HasPromise());
+  MOZ_DIAGNOSTIC_ASSERT(aTarget.IsVideoOnly() || !mAudio.HasPromise());
   MOZ_DIAGNOSTIC_ASSERT(mPendingSeekTime.isNothing());
   MOZ_DIAGNOSTIC_ASSERT(mVideo.mTimeThreshold.isNothing());
-  MOZ_DIAGNOSTIC_ASSERT(mAudio.mTimeThreshold.isNothing());
+  MOZ_DIAGNOSTIC_ASSERT(aTarget.IsVideoOnly() || mAudio.mTimeThreshold.isNothing());
 
   if (!mInfo.mMediaSeekable && !mInfo.mMediaSeekableOnlyInBufferedRanges) {
     LOG("Seek() END (Unseekable)");
     return SeekPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
   }
 
   if (mShutdown) {
     return SeekPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);