diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 5af18d11b5184805bf7a01c5d94d0759b21c4992..2a167658bb958ae3a302bd80a46649416c697183 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -192,10 +192,10 @@ static int pack_sg_list(struct scatterlist *sg, int start,
 		s = rest_of_page(data);
 		if (s > count)
 			s = count;
+		BUG_ON(index > limit);
 		sg_set_buf(&sg[index++], data, s);
 		count -= s;
 		data += s;
-		BUG_ON(index > limit);
 	}
 
 	return index-start;