diff --git a/upgrade-cluster.yml b/upgrade-cluster.yml
index 50a856ac0..a377a625a 100644
--- a/upgrade-cluster.yml
+++ b/upgrade-cluster.yml
@@ -24,6 +24,7 @@
 
 - hosts: k8s-cluster:etcd:calico-rr
   any_errors_fatal: "{{ any_errors_fatal | default(true) }}"
+  serial: "{{ serial | default('20%') }}"
   roles:
     - { role: kubespray-defaults}
     - { role: kubernetes/preinstall, tags: preinstall }