diff --git a/calendar/js/app.js b/calendar/js/app.js
index 616e286ddd..c8430ade25 100644
--- a/calendar/js/app.js
+++ b/calendar/js/app.js
@@ -1292,7 +1292,7 @@ var CalendarApp = /** @class */ (function (_super) {
             var end = widget.getRoot().getDOMWidgetById('end');
             var start_time = new Date(widget.getValue());
             var end_time = new Date(end.getValue());
-            if (end_time <= start_time) {
+            if (end.getValue() && end_time <= start_time) {
                 start_time.setMinutes(start_time.getMinutes() + 1);
                 end.set_value(start_time);
             }
diff --git a/calendar/js/app.ts b/calendar/js/app.ts
index b43d831a17..a0a19fe5fc 100644
--- a/calendar/js/app.ts
+++ b/calendar/js/app.ts
@@ -1352,7 +1352,7 @@ class CalendarApp extends EgwApp
 			let end = <et2_date> widget.getRoot().getDOMWidgetById('end');
 			let start_time = new Date(widget.getValue());
 			let end_time = new Date(end.getValue());
-			if(end_time <= start_time)
+			if(end.getValue() && end_time <= start_time)
 			{
 				start_time.setMinutes(start_time.getMinutes() + 1);
 				end.set_value(start_time);