diff --git a/third_party/terraform/resources/resource_compute_region_instance_group_manager.go b/third_party/terraform/resources/resource_compute_region_instance_group_manager.go
index 2f4cc6d72323..d2e57bd417db 100644
--- a/third_party/terraform/resources/resource_compute_region_instance_group_manager.go
+++ b/third_party/terraform/resources/resource_compute_region_instance_group_manager.go
@@ -38,7 +38,7 @@ func resourceComputeRegionInstanceGroupManager() *schema.Resource {
 
 			"instance_template": {
 				Type:     schema.TypeString,
-				Optional: true,
+				Computed: true,
 				Removed:  "This field has been replaced by `version.instance_template` in 3.0.0",
 			},