diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 39085e7dd6d2..7dc2a5a127e8 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1727,6 +1727,7 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 	r10_bio->mddev = mddev;
 	r10_bio->state = 0;
 	r10_bio->sectors = 0;
+	r10_bio->read_slot = -1;
 	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
 	wait_blocked_dev(mddev, r10_bio);