diff --git a/libavformat/webm_chunk.c b/libavformat/webm_chunk.c
index f8dbaa3339..3f91162da7 100644
--- a/libavformat/webm_chunk.c
+++ b/libavformat/webm_chunk.c
@@ -96,7 +96,7 @@ static int get_chunk_filename(AVFormatContext *s, int is_header, char *filename)
             av_log(oc, AV_LOG_ERROR, "No header filename provided\n");
             return AVERROR(EINVAL);
         }
-        av_strlcpy(filename, wc->header_filename, strlen(wc->header_filename) + 1);
+        av_strlcpy(filename, wc->header_filename, MAX_FILENAME_SIZE);
     } else {
         if (av_get_frame_filename(filename, MAX_FILENAME_SIZE,
                                   s->filename, wc->chunk_index - 1) < 0) {