diff --git a/cluster/gce/configure-vm.sh b/cluster/gce/configure-vm.sh
index 256406bd9e9..527b6cee035 100644
--- a/cluster/gce/configure-vm.sh
+++ b/cluster/gce/configure-vm.sh
@@ -362,7 +362,7 @@ EOF
   kube_proxy_kubeconfig_file="/srv/salt-overlay/salt/kube-proxy/kubeconfig"
   if [ ! -e "${kube_proxy_kubeconfig_file}" ]; then
     mkdir -p /srv/salt-overlay/salt/kube-proxy
-    if [[ ! -z "${CA_CERT}" ]]; then
+    if [[ ! -z "${CA_CERT:-}" ]]; then
       (umask 077;
         cat > "${kube_proxy_kubeconfig_file}" <<EOF
 apiVersion: v1