diff --git a/libavcodec/h264.c b/libavcodec/h264.c
index eef34db57dcd2be742d9c1ae82259c9dffd558a5..368ce352faedabd32d6f90e2b42ffd1373233ba8 100644
--- a/libavcodec/h264.c
+++ b/libavcodec/h264.c
@@ -2268,6 +2268,7 @@ static int frame_start(H264Context *h){
 
     s->current_picture_ptr->field_poc[0]=
     s->current_picture_ptr->field_poc[1]= INT_MAX;
+    assert(s->current_picture_ptr->long_ref==0);
 
     return 0;
 }