diff --git a/calendar/js/et2_widget_event.js b/calendar/js/et2_widget_event.js
index d3c7a4daf8..3836a51d97 100644
--- a/calendar/js/et2_widget_event.js
+++ b/calendar/js/et2_widget_event.js
@@ -171,7 +171,7 @@ var et2_calendar_event = /** @class */ (function (_super) {
         var value = event === null ? null : jQuery.extend({}, event);
         var parent = this.getParent();
         var parent_owner = parent.getDOMNode(parent).dataset['owner'] || parent.getParent().options.owner;
-        if (parent_owner.indexOf(',')) {
+        if (parent_owner.indexOf(',') >= 0) {
             parent_owner = parent_owner.split(',');
         }
         // Make sure id is a string, check values
diff --git a/calendar/js/et2_widget_event.ts b/calendar/js/et2_widget_event.ts
index e768337673..c9d1a06f0c 100644
--- a/calendar/js/et2_widget_event.ts
+++ b/calendar/js/et2_widget_event.ts
@@ -211,7 +211,7 @@ export class et2_calendar_event extends et2_valueWidget implements et2_IDetached
 		const value = event === null ? null : jQuery.extend({}, event);
 		let parent = <et2_DOMWidget>this.getParent();
 		let parent_owner = parent.getDOMNode(parent).dataset['owner'] || parent.getParent().options.owner;
-		if(parent_owner.indexOf(','))
+		if(parent_owner.indexOf(',') >= 0)
 		{
 			parent_owner = parent_owner.split(',');
 		}