diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
index 9cb6295185..eddaadc837 100644
--- a/libavcodec/h263dec.c
+++ b/libavcodec/h263dec.c
@@ -322,7 +322,7 @@ static int decode_slice(MpegEncContext *s){
 
 int ff_h263_decode_frame(AVCodecContext *avctx,
                              void *data, int *data_size,
-                             uint8_t *buf, int buf_size)
+                             const uint8_t *buf, int buf_size)
 {
     MpegEncContext *s = avctx->priv_data;
     int ret;
diff --git a/libavcodec/mpegvideo.h b/libavcodec/mpegvideo.h
index 7a2198dc47..c54a4bab20 100644
--- a/libavcodec/mpegvideo.h
+++ b/libavcodec/mpegvideo.h
@@ -817,7 +817,7 @@ int ff_h261_get_picture_format(int width, int height);
 int ff_h263_decode_init(AVCodecContext *avctx);
 int ff_h263_decode_frame(AVCodecContext *avctx,
                              void *data, int *data_size,
-                             uint8_t *buf, int buf_size);
+                             const uint8_t *buf, int buf_size);
 int ff_h263_decode_end(AVCodecContext *avctx);
 void h263_encode_mb(MpegEncContext *s,
                     DCTELEM block[6][64],