Fix #2901

builtin/providers/google/resource_compute_instance_template.go

@@ -261,7 +261,7 @@ func buildDisks(d *schema.ResourceData, meta interface{}) ([]*compute.AttachedDi
 				disk.InitializeParams.DiskName = v.(string)
 			}
 			if v, ok := d.GetOk(prefix + ".disk_size_gb"); ok {
-				disk.InitializeParams.DiskSizeGb = v.(int64)
+				disk.InitializeParams.DiskSizeGb = int64(v.(int))
 			}
 			disk.InitializeParams.DiskType = "pd-standard"
 			if v, ok := d.GetOk(prefix + ".disk_type"); ok {

builtin/providers/google/resource_compute_instance_template_test.go

@@ -269,6 +269,7 @@ resource "google_compute_instance_template" "foobar" {
 	disk {
 		source_image = "debian-7-wheezy-v20140814"
 		auto_delete = true
+		disk_size_gb = 100
 		boot = true
 	}