diff --git a/libavformat/srtdec.c b/libavformat/srtdec.c
index 0af3714196..cabbb62076 100644
--- a/libavformat/srtdec.c
+++ b/libavformat/srtdec.c
@@ -31,7 +31,7 @@ typedef struct {
 
 static int srt_probe(AVProbeData *p)
 {
-    unsigned char *ptr = p->buf;
+    const unsigned char *ptr = p->buf;
     int i, v, num = 0;
 
     if (AV_RB24(ptr) == 0xEFBBBF)