diff --git a/src/applications/people/event/PhabricatorPeopleHovercardEventListener.php b/src/applications/people/event/PhabricatorPeopleHovercardEventListener.php
--- a/src/applications/people/event/PhabricatorPeopleHovercardEventListener.php
+++ b/src/applications/people/event/PhabricatorPeopleHovercardEventListener.php
@@ -37,7 +37,9 @@
       $hovercard->addField(pht('Account'), pht('Disabled'));
     } else if (!$user->isUserActivated()) {
       $hovercard->addField(pht('Account'), pht('Not Activated'));
-    } else {
+    } else if (PhabricatorApplication::isClassInstalledForViewer(
+        'PhabricatorApplicationCalendar',
+        $viewer)) {
       $statuses = id(new PhabricatorCalendarEvent())->loadCurrentStatuses(
         array($user->getPHID()));
       if ($statuses) {