diff --git a/block/bio.c b/block/bio.c
index 4f93345c6a82..68972e3d3f5c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -155,7 +155,7 @@ out:
 
 unsigned int bvec_nr_vecs(unsigned short idx)
 {
-	return bvec_slabs[idx].nr_vecs;
+	return bvec_slabs[--idx].nr_vecs;
 }
 
 void bvec_free(mempool_t *pool, struct bio_vec *bv, unsigned int idx)