diff --git a/calendar/js/app.ts b/calendar/js/app.ts
index ef2cf7388c..80bda93d8c 100644
--- a/calendar/js/app.ts
+++ b/calendar/js/app.ts
@@ -3763,7 +3763,7 @@ export class CalendarApp extends EgwApp
 	 * @param event
 	 * @return Promise| null
 	 */
-	_fetch_group_members(event) : Promise<any> | null
+	async _fetch_group_members(event) : Promise<any> | null
 	{
 		let groups = [];
 		let option_owner = null;