diff --git a/libavcodec/h264.c b/libavcodec/h264.c
index 7d57cd8d269bb9412569a4ab6c564aed1cfb8199..e623faab5b97b1ad84cca2dfdb720944ce50adaf 100644
--- a/libavcodec/h264.c
+++ b/libavcodec/h264.c
@@ -6119,7 +6119,7 @@ static void filter_mb_fast( H264Context *h, int mb_x, int mb_y, uint8_t *img_y,
     mb_xy = h->mb_xy;
 
     if(mb_x==0 || mb_y==mb_y_firstrow || !s->dsp.h264_loop_filter_strength || h->pps.chroma_qp_diff ||
-1 ||
+        !(s->flags2 & CODEC_FLAG2_FAST) || //FIXME filter_mb_fast is broken, thus hasto be, but should not under CODEC_FLAG2_FAST
        (h->deblocking_filter == 2 && (h->slice_table[mb_xy] != h->slice_table[h->top_mb_xy] ||
                                       h->slice_table[mb_xy] != h->slice_table[mb_xy - 1]))) {
         filter_mb(h, mb_x, mb_y, img_y, img_cb, img_cr, linesize, uvlinesize);