diff --git a/calendar/js/app.js b/calendar/js/app.js
index b6be0479dd..59a22a23dc 100644
--- a/calendar/js/app.js
+++ b/calendar/js/app.js
@@ -3568,7 +3568,12 @@ var CalendarApp = /** @class */ (function (_super) {
                 email: egw.user('account_email'),
                 cal_id: _data.id,
                 title: _data.title
-            }, _data.start, _data.end, {
+            },
+            // Dates are user time, but we told javascript it was UTC.
+            // Send just the timestamp (as a string) with no timezone
+            _data.start.toJSON().slice(0, -1),
+            _data.end.toJSON().slice(0, -1),
+            {
                 participants: Object.keys(_data.participants).filter(function (v) { return v.match(/^[0-9]/); })
             }], function (_value) {
             if (_value) {
diff --git a/calendar/js/app.ts b/calendar/js/app.ts
index 2421e9938b..fe7221f32c 100644
--- a/calendar/js/app.ts
+++ b/calendar/js/app.ts
@@ -4429,7 +4429,12 @@ class CalendarApp extends EgwApp
 					email:egw.user('account_email'),
 					cal_id:_data.id,
 					title: _data.title
-				}, _data.start, _data.end, {
+				},
+			    // Dates are user time, but we told javascript it was UTC.
+			    // Send just the timestamp (as a string) with no timezone
+                _data.start.toJSON().slice(0,-1),
+                _data.end.toJSON().slice(0,-1),
+				{
 					participants:Object.keys(_data.participants).filter(v => {return v.match(/^[0-9]/)})
 				}], function(_value){
 					if (_value)