diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index e549392e0ea5..0837b17e1798 100644
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -699,7 +699,7 @@ static int log_writes_map(struct dm_target *ti, struct bio *bio)
 	if (discard_bio)
 		alloc_size = sizeof(struct pending_block);
 	else
-		alloc_size = sizeof(struct pending_block) + sizeof(struct bio_vec) * bio_segments(bio);
+		alloc_size = struct_size(block, vecs, bio_segments(bio));
 
 	block = kzalloc(alloc_size, GFP_NOIO);
 	if (!block) {