diff --git a/libavcodec/zmbv.c b/libavcodec/zmbv.c
index 76d8b654a3..1eb8ef00a1 100644
--- a/libavcodec/zmbv.c
+++ b/libavcodec/zmbv.c
@@ -391,7 +391,7 @@ static int zmbv_decode_intra(ZmbvContext *c)
     return 0;
 }
 
-static int decode_frame(AVCodecContext *avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
+static int decode_frame(AVCodecContext *avctx, void *data, int *data_size, const uint8_t *buf, int buf_size)
 {
     ZmbvContext * const c = avctx->priv_data;
     uint8_t *outptr;