diff --git a/cluster/gke/util.sh b/cluster/gke/util.sh
index e0f57f49c25..eeb20bad790 100755
--- a/cluster/gke/util.sh
+++ b/cluster/gke/util.sh
@@ -318,7 +318,7 @@ function detect-node-instance-groups {
   ALL_INSTANCE_GROUP_URLS=${urls[*]}
   NODE_INSTANCE_GROUPS=()
   for url in "${urls[@]:-}"; do
-    local igm_zone=$(expr match ${url} '.*/zones/\([a-z0-9-]*\)/')
+    local igm_zone=$(expr ${url} : '.*/zones/\([a-z0-9-]*\)/')
     if [[ "${igm_zone}" == "${ZONE}" ]]; then
       NODE_INSTANCE_GROUPS+=("${url##*/}")
     fi