diff --git a/libavcodec/tscc.c b/libavcodec/tscc.c
index 40013ae9a7..30bb19f976 100644
--- a/libavcodec/tscc.c
+++ b/libavcodec/tscc.c
@@ -182,10 +182,10 @@ static int decode_rle(CamtasiaContext *c, unsigned int srcsize)
  * Decode a frame
  *
  */
-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)
 {
     CamtasiaContext * const c = avctx->priv_data;
-    unsigned char *encoded = (unsigned char *)buf;
+    const unsigned char *encoded = buf;
     unsigned char *outptr;
 #ifdef CONFIG_ZLIB
     int zret; // Zlib return code