diff --git a/libavformat/internal.h b/libavformat/internal.h
index 98341ba217..f1ae7db365 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -121,7 +121,9 @@ typedef struct FFFormatContext {
     AVPacket *parse_pkt;
 
     /**
-     * Used to hold temporary packets.
+     * Used to hold temporary packets for the generic demuxing code.
+     * When muxing, it may be used by muxers to hold packets (even
+     * permanent ones).
      */
     AVPacket *pkt;
     /**
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 3d007ec943..be9ba88365 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -1292,6 +1292,7 @@ int av_write_trailer(AVFormatContext *s)
     if (s->oformat->priv_class)
         av_opt_free(s->priv_data);
     av_freep(&s->priv_data);
+    av_packet_unref(si->pkt);
     return ret;
 }