diff --git a/libavcodec/smc.c b/libavcodec/smc.c
index 3cd5e53f5f..71d85f030a 100644
--- a/libavcodec/smc.c
+++ b/libavcodec/smc.c
@@ -83,7 +83,7 @@ static void smc_decode_stream(SmcContext *s)
     int stride = s->frame.linesize[0];
     int i;
     int chunk_size;
-    int buf_size = (int) (s->gb.buffer_end - s->gb.buffer_start);
+    int buf_size = bytestream2_size(&s->gb);
     unsigned char opcode;
     int n_blocks;
     unsigned int color_flags;