diff --git a/libavcodec/mpegvideo_xvmc.c b/libavcodec/mpegvideo_xvmc.c
index cbb51c21e7a2a67dc551230a6e2fe558c9db0357..cc22a262c0bf6d5dfefa362989939d98810c45b6 100644
--- a/libavcodec/mpegvideo_xvmc.c
+++ b/libavcodec/mpegvideo_xvmc.c
@@ -285,6 +285,8 @@ void ff_xvmc_decode_mb(MpegEncContext *s)
 
     assert(render->filled_mv_blocks_num     <= render->total_number_of_mv_blocks);
     assert(render->next_free_data_block_num <= render->total_number_of_data_blocks);
+    /*The above conditions should not be able to fail as long as this function is used
+    and following if() automatically call callback to free blocks. */
 
 
     if (render->filled_mv_blocks_num >= render->total_number_of_mv_blocks)