diff --git a/drivers/md/md.c b/drivers/md/md.c
index 27506302eb7a..dd59d71ade2f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3834,7 +3834,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
 				err = -EBUSY;
 		}
 		spin_unlock(&mddev->lock);
-		return err;
+		return err ?: len;
 	}
 	err = mddev_lock(mddev);
 	if (err)