diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php b/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
--- a/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
@@ -47,6 +47,9 @@
             PhabricatorPolicyCapability::CAN_EDIT,
           ))
         ->executeOne();
+      if (!$status) {
+        return new Aphront404Response();
+      }
 
       $end_time->setValue($status->getDateTo());
       $start_time->setValue($status->getDateFrom());