diff --git a/libavcodec/h261dec.c b/libavcodec/h261dec.c
index f35f79185e..264a7d3f58 100644
--- a/libavcodec/h261dec.c
+++ b/libavcodec/h261dec.c
@@ -540,7 +540,7 @@ static int get_consumed_bytes(MpegEncContext *s, int buf_size){
 
 static int h261_decode_frame(AVCodecContext *avctx,
                              void *data, int *data_size,
-                             uint8_t *buf, int buf_size)
+                             const uint8_t *buf, int buf_size)
 {
     H261Context *h= avctx->priv_data;
     MpegEncContext *s = &h->s;