diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 78c483c25c..f918d20a61 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -4648,7 +4648,7 @@ void av_packet_free_side_data(AVPacket *pkt);
  *
  * @see av_packet_unref
  *
- * @param dst Destination packet
+ * @param dst Destination packet. Will be completely overwritten.
  * @param src Source packet
  *
  * @return 0 on success, a negative AVERROR on error.
diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
index b5667659fd..132567bc2d 100644
--- a/libavcodec/avpacket.c
+++ b/libavcodec/avpacket.c
@@ -615,6 +615,7 @@ int av_packet_ref(AVPacket *dst, const AVPacket *src)
         return ret;
 
     if (!src->buf) {
+        dst->buf = NULL;
         ret = packet_alloc(&dst->buf, src->size);
         if (ret < 0)
             goto fail;