diff --git a/libavcodec/xl.c b/libavcodec/xl.c
index e7dd7923fb..b48a369b8b 100644
--- a/libavcodec/xl.c
+++ b/libavcodec/xl.c
@@ -40,7 +40,7 @@ static const int xl_table[32] = {
 
 static int decode_frame(AVCodecContext *avctx,
                         void *data, int *data_size,
-                        uint8_t *buf, int buf_size)
+                        const uint8_t *buf, int buf_size)
 {
     VideoXLContext * const a = avctx->priv_data;
     AVFrame * const p= (AVFrame*)&a->pic;