diff --git a/libavformat/webm_chunk.c b/libavformat/webm_chunk.c
index f0e3eacdf1..67db01e19e 100644
--- a/libavformat/webm_chunk.c
+++ b/libavformat/webm_chunk.c
@@ -82,7 +82,7 @@ static int chunk_mux_init(AVFormatContext *s)
     return 0;
 }
 
-static int get_chunk_filename(AVFormatContext *s, int is_header, char *filename)
+static int get_chunk_filename(AVFormatContext *s, int is_header, char filename[MAX_FILENAME_SIZE])
 {
     WebMChunkContext *wc = s->priv_data;
     AVFormatContext *oc = wc->avf;