diff --git a/libavformat/mlvdec.c b/libavformat/mlvdec.c
index d387c871ee..ded8196af2 100644
--- a/libavformat/mlvdec.c
+++ b/libavformat/mlvdec.c
@@ -77,7 +77,7 @@ static int check_file_header(AVIOContext *pb, uint64_t guid)
     return 0;
 }
 
-static void read_string(AVFormatContext *avctx, AVIOContext *pb, const char *tag, int size)
+static void read_string(AVFormatContext *avctx, AVIOContext *pb, const char *tag, unsigned size)
 {
     char * value = av_malloc(size + 1);
     if (!value) {