diff --git a/calendar/event.php b/calendar/event.php
index 7093c95290f..9d5fd564d8f 100644
--- a/calendar/event.php
+++ b/calendar/event.php
@@ -378,7 +378,7 @@
                     $form->timestart = make_timestamp($cal_y, $cal_m, 1, 0, 0, 0);
                 }
             }
-            if($form->timestart < 0) {
+            if(!isset($form->timestart) or $form->timestart < 0) {
                 $form->timestart = time();
             }