diff --git a/libavformat/format.c b/libavformat/format.c
index fd81d7a132..ffddb13782 100644
--- a/libavformat/format.c
+++ b/libavformat/format.c
@@ -175,7 +175,7 @@ AVInputFormat *av_probe_input_format3(AVProbeData *pd, int is_opened,
     const static uint8_t zerobuffer[AVPROBE_PADDING_SIZE];
 
     if (!lpd.buf)
-        lpd.buf = zerobuffer;
+        lpd.buf = (unsigned char *) zerobuffer;
 
     if (lpd.buf_size > 10 && ff_id3v2_match(lpd.buf, ID3v2_DEFAULT_MAGIC)) {
         int id3len = ff_id3v2_tag_len(lpd.buf);