diff --git a/libavformat/mm.c b/libavformat/mm.c
index 6c621ab..1868e90 100644
--- a/libavformat/mm.c
+++ b/libavformat/mm.c
@@ -162,7 +162,6 @@
         case MM_TYPE_AUDIO :
             if (av_get_packet(s->pb, pkt, length)<0)
                 return AVERROR(ENOMEM);
-            pkt->size = length;
             pkt->stream_index = 1;
             pkt->pts = mm->audio_pts++;
             return 0;