diff --git a/libavformat/mov.c b/libavformat/mov.c
index a709033abd..feec372a61 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -1979,6 +1979,10 @@ static int mov_read_stco(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     MOVStreamContext *sc;
     unsigned int i, entries;
 
+    if (c->trak_index < 0) {
+        av_log(c->fc, AV_LOG_WARNING, "STCO outside TRAK\n");
+        return 0;
+    }
     if (c->fc->nb_streams < 1)
         return 0;
     st = c->fc->streams[c->fc->nb_streams-1];