--- a/dom/media/platforms/wrappers/H264Converter.cpp
+++ b/dom/media/platforms/wrappers/H264Converter.cpp
@@ -69,16 +69,23 @@ H264Converter::Decode(MediaRawData* aSam
   if (!mp4_demuxer::AnnexB::ConvertSampleToAVCC(aSample)) {
     // We need AVCC content to be able to later parse the SPS.
     // This is a no-op if the data is already AVCC.
     return DecodePromise::CreateAndReject(
       MediaResult(NS_ERROR_OUT_OF_MEMORY, RESULT_DETAIL("ConvertSampleToAVCC")),
       __func__);
   }
 
+  if (!mp4_demuxer::AnnexB::IsAVCC(aSample)) {
+    return DecodePromise::CreateAndReject(
+      MediaResult(NS_ERROR_DOM_MEDIA_FATAL_ERR,
+                  RESULT_DETAIL("Invalid H264 content")),
+      __func__);
+  }
+
   nsresult rv;
   if (!mDecoder) {
     // It is not possible to create an AVCC H264 decoder without SPS.
     // As such, creation will fail if the extra_data just extracted doesn't
     // contain a SPS.
     rv = CreateDecoderAndInit(aSample);
     if (rv == NS_ERROR_NOT_INITIALIZED) {
       // We are missing the required SPS to create the decoder.