diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index f7b15b77a5..fa6821ca1c 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1090,7 +1090,7 @@ static AVStream *get_subtitle_pkt(AVFormatContext *s, AVStream *next_st,
     return sub_st;
 }
 
-static int get_stream_idx(unsigned *d)
+static int get_stream_idx(const unsigned *d)
 {
     if (d[0] >= '0' && d[0] <= '9' &&
         d[1] >= '0' && d[1] <= '9') {