diff --git a/src/applications/conpherence/controller/ConpherenceUpdateController.php b/src/applications/conpherence/controller/ConpherenceUpdateController.php
--- a/src/applications/conpherence/controller/ConpherenceUpdateController.php
+++ b/src/applications/conpherence/controller/ConpherenceUpdateController.php
@@ -328,7 +328,7 @@
       ->executeOne();
 
     $non_update = false;
-    $participant = $conpherence->getParticipant($user->getPHID());
+    $participant = $conpherence->getParticipantIfExists($user->getPHID());
 
     if ($need_transactions && $conpherence->getTransactions()) {
       $data = ConpherenceTransactionRenderer::renderTransactions(
@@ -336,7 +336,7 @@
         $conpherence);
       $key = PhabricatorConpherenceColumnMinimizeSetting::SETTINGKEY;
       $minimized = $user->getUserSetting($key);
-      if (!$minimized) {
+      if (!$minimized && $participant) {
         $participant->markUpToDate($conpherence);
       }
     } else if ($need_transactions) {