diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index b68ea4db10..878da12b11 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -31,9 +31,9 @@
 //#define DEBUG
 
 typedef struct PNGDecContext {
-    uint8_t *bytestream;
-    uint8_t *bytestream_start;
-    uint8_t *bytestream_end;
+    const uint8_t *bytestream;
+    const uint8_t *bytestream_start;
+    const uint8_t *bytestream_end;
     AVFrame picture;
 
     int state;
@@ -312,7 +312,7 @@ static int png_decode_idat(PNGDecContext *s, int length)
 
 static int decode_frame(AVCodecContext *avctx,
                         void *data, int *data_size,
-                        uint8_t *buf, int buf_size)
+                        const uint8_t *buf, int buf_size)
 {
     PNGDecContext * const s = avctx->priv_data;
     AVFrame *picture = data;