diff --git a/src/owlboardApi/trainTimetable.ts b/src/owlboardApi/trainTimetable.ts
index 770d7f2..6e59e83 100644
--- a/src/owlboardApi/trainTimetable.ts
+++ b/src/owlboardApi/trainTimetable.ts
@@ -11,7 +11,7 @@ export interface OB_TrainTT_service {
     scheduleEnd: Date;
     daysRun: string[];
     stops: OB_TrainTT_stopDetail[];
-    pis: OB_Pis_SimpleObject;
+    pis?: OB_Pis_SimpleObject;
 }
 
 export interface OB_TrainTT_stopDetail {