diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index cccfdb41b6..36b29e2d8d 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1463,6 +1463,7 @@ static int mkv_write_chapters(AVFormatContext *s)
             av_log(s, AV_LOG_ERROR,
                    "Invalid chapter start (%"PRId64") or end (%"PRId64").\n",
                    chapterstart, chapterend);
+            ffio_free_dyn_buf(&dyn_cp);
             return AVERROR_INVALIDDATA;
         }