diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index f6eb71ec0f..3105d339ca 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -944,7 +944,7 @@ start_sync:
         n= get_stream_idx(d+2);
         av_dlog(s, "%X %X %X %X %X %X %X %X %"PRId64" %u %d\n",
                 d[0], d[1], d[2], d[3], d[4], d[5], d[6], d[7], i, size, n);
-        if(i + (uint64_t)size > avi->fsize || d[0] > 127)
+        if(i*(avi->io_fsize>0) + (uint64_t)size > avi->fsize || d[0] > 127)
             continue;
 
         //parse ix##