diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 23c6960e94a4..2bdd1e3e7007 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -118,7 +118,7 @@ struct btrfs_ioctl_vol_args_v2 {
 	};
 	union {
 		char name[BTRFS_SUBVOL_NAME_MAX + 1];
-		u64 devid;
+		__u64 devid;
 	};
 };