diff --git a/lib/models/calendar/CalendarDateAssignment.class.php b/lib/models/calendar/CalendarDateAssignment.class.php
index 8eb536f90f70cfb3ca390566d01e412ef253b4ce..37e3b66026e0d846c3b91af64062f9efc2ea6d56 100644
--- a/lib/models/calendar/CalendarDateAssignment.class.php
+++ b/lib/models/calendar/CalendarDateAssignment.class.php
@@ -217,6 +217,11 @@ class CalendarDateAssignment extends SimpleORMap implements Event
         bool $with_declined = false
     ) : array
     {
+        // use always the server's timezone
+        $local_timezone = (new DateTime())->getTimezone();
+        $begin->setTimezone($local_timezone);
+        $end->setTimezone($local_timezone);
+
         // one whole day as minimum (begin and end time stamp at the same day)
         $begin->modify('midnight');
         $end->modify('tomorrow -1 second');