diff --git a/libavformat/mux.c b/libavformat/mux.c
index 9aee224d1f..2a28fd668a 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -624,7 +624,7 @@ int av_write_trailer(AVFormatContext *s)
     if (s->oformat->write_trailer)
         ret = s->oformat->write_trailer(s);
 
-    if (!(s->oformat->flags & AVFMT_NOFILE))
+    if (!(s->oformat->flags & AVFMT_NOFILE) && s->pb)
         avio_flush(s->pb);
 
 fail: