diff --git a/libavcodec/h264.c b/libavcodec/h264.c
index f17c592df692ac8d24f489b8e18b5cced4e0e3c2..395ae1c5031f0cecbbd12d90ff5487c806503bd4 100644
--- a/libavcodec/h264.c
+++ b/libavcodec/h264.c
@@ -4234,7 +4234,7 @@ static int decode_slice_header(H264Context *h){
             s->picture_structure= PICT_TOP_FIELD + get_bits1(&s->gb); //bottom_field_flag
         } else {
             s->picture_structure= PICT_FRAME;
-            first_mb_in_slice <<= 1;
+            first_mb_in_slice <<= h->sps.mb_aff;
             h->mb_aff_frame = h->sps.mb_aff;
         }
     }