diff --git a/libavformat/webm_chunk.c b/libavformat/webm_chunk.c
index 3dfef4bb0e..265e6ec845 100644
--- a/libavformat/webm_chunk.c
+++ b/libavformat/webm_chunk.c
@@ -93,7 +93,7 @@ static int get_chunk_filename(AVFormatContext *s, int is_header, char *filename)
         if (!wc->header_filename) {
             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) {