diff --git a/schema-types.ts b/schema-types.ts
index a60ac1d..5da653b 100644
--- a/schema-types.ts
+++ b/schema-types.ts
@@ -4,8 +4,8 @@ import { tags } from "typia";
 /* messages ***************************************************************************************/
 
 export type SimToCmMessage = {
-  message: Message,
-  stressLevel: Range<0, 1>,
+  message?: Message,
+  stressLevel?: Range<0, 1>,
 };
 
 export type Message = RequestApprovalToAttack | AcaFuelLow | MissileToOwnshipDetected | AcaDefect | AcaHeadingToBase;