diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 8034fbd6190ce647ec2feb6a281e4bb32b406f8e..636bae0405e8167edcec328e5759b3f949dd0876 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2710,7 +2710,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 		    || disk_idx < 0)
 			continue;
 		if (test_bit(Replacement, &rdev->flags))
-			disk = conf->mirrors + conf->raid_disks + disk_idx;
+			disk = conf->mirrors + mddev->raid_disks + disk_idx;
 		else
 			disk = conf->mirrors + disk_idx;