--- a/dom/media/mediasource/TrackBuffer.cpp
+++ b/dom/media/mediasource/TrackBuffer.cpp
@@ -211,24 +211,22 @@ TrackBuffer::AppendData(LargeDataBuffer*
          (mCurrentDecoder && mCurrentDecoder->WasTrimmed()))) {
       MSE_DEBUG("TrackBuffer(%p)::AppendData: Data last=[%lld, %lld] overlaps [%lld, %lld]",
                 this, mLastStartTimestamp, mLastEndTimestamp.value(), start, end);
 
       if (!newInitData) {
         // This data is earlier in the timeline than data we have already
         // processed or not continuous, so we must create a new decoder
         // to handle the decoding.
-        if (!decoders.NewDecoder(aTimestampOffset)) {
+        if (!hadCompleteInitData || !decoders.NewDecoder(aTimestampOffset)) {
           mInitializationPromise.Reject(NS_ERROR_FAILURE, __func__);
           return p;
         }
-        if (hadCompleteInitData) {
-          MSE_DEBUG("TrackBuffer(%p)::AppendData: Decoder marked as initialized.", this);
-          AppendDataToCurrentResource(oldInit, 0);
-        }
+        MSE_DEBUG("TrackBuffer(%p)::AppendData: Decoder marked as initialized.", this);
+        AppendDataToCurrentResource(oldInit, 0);
       }
       mLastStartTimestamp = start;
     } else {
       MSE_DEBUG("TrackBuffer(%p)::AppendData: Segment last=[%lld, %lld] [%lld, %lld]",
                 this, mLastStartTimestamp, mLastEndTimestamp ? mLastEndTimestamp.value() : 0, start, end);
     }
     mLastEndTimestamp.reset();
     mLastEndTimestamp.emplace(end);