diff --git a/modules/instance_template/variables.tf b/modules/instance_template/variables.tf
index 160935d7..86c4baf2 100644
--- a/modules/instance_template/variables.tf
+++ b/modules/instance_template/variables.tf
@@ -80,7 +80,7 @@ variable "maintenance_interval" {
   default     = null
   validation {
     condition     = var.maintenance_interval == null || var.maintenance_interval == "PERIODIC"
-    error_message = "var.maintenance_interval must be set to null or \"PERIODIC\""
+    error_message = "var.maintenance_interval must be set to null or \"PERIODIC\"."
   }
 }