diff --git a/deploy/modules/gcp/tidb-cluster/main.tf b/deploy/modules/gcp/tidb-cluster/main.tf
index c4100ae5aa..b6dd957a25 100644
--- a/deploy/modules/gcp/tidb-cluster/main.tf
+++ b/deploy/modules/gcp/tidb-cluster/main.tf
@@ -125,7 +125,7 @@ resource "google_container_node_pool" "monitor_pool" {
 }
 
 locals {
-  num_availability_zones = length(data.google_compute_zones.available)
+  num_availability_zones = length(data.google_compute_zones.available.names)
 }
 
 module "tidb-cluster" {