diff --git a/dom/media/mediasource/TrackBuffersManager.cpp b/dom/media/mediasource/TrackBuffersManager.cpp
index 359850f1836b..a99a17685a0b 100644
--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -2624,6 +2624,7 @@ const MediaRawData* TrackBuffersManager::GetSample(TrackInfo::TrackType aTrack,
   const RefPtr<MediaRawData>& sample = track[aIndex];
   if (!aIndex || sample->mTimecode <= aExpectedDts + aFuzz ||
       sample->mTime <= aExpectedPts + aFuzz) {
+    MOZ_DIAGNOSTIC_ASSERT(sample->HasValidTime());
     return sample;
   }