diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
index 9ed4bdb1b4..e690583010 100644
--- a/libavcodec/h263dec.c
+++ b/libavcodec/h263dec.c
@@ -618,12 +618,12 @@ retry:
         return -1;
 
     if (CONFIG_MPEG4_VDPAU_DECODER && (s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU)) {
-        ff_vdpau_mpeg4_decode_picture(s, buf, buf_size);
+        ff_vdpau_mpeg4_decode_picture(s, s->gb.buffer, s->gb.buffer_end - s->gb.buffer);
         goto frame_end;
     }
 
     if (avctx->hwaccel) {
-        if (avctx->hwaccel->start_frame(avctx, buf, buf_size) < 0)
+        if (avctx->hwaccel->start_frame(avctx, s->gb.buffer, s->gb.buffer_end - s->gb.buffer) < 0)
             return -1;
     }