diff --git a/src/applications/notification/query/PhabricatorNotificationQuery.php b/src/applications/notification/query/PhabricatorNotificationQuery.php
index 6eea54a0de..4ceca2e1d4 100644
--- a/src/applications/notification/query/PhabricatorNotificationQuery.php
+++ b/src/applications/notification/query/PhabricatorNotificationQuery.php
@@ -1,169 +1,181 @@
 <?php
 
 /**
  * @task config Configuring the Query
  * @task exec   Query Execution
  */
 final class PhabricatorNotificationQuery
   extends PhabricatorCursorPagedPolicyAwareQuery {
 
   private $userPHIDs;
   private $keys;
   private $unread;
 
 
 /* -(  Configuring the Query  )---------------------------------------------- */
 
 
   public function withUserPHIDs(array $user_phids) {
     $this->userPHIDs = $user_phids;
     return $this;
   }
 
   public function withKeys(array $keys) {
     $this->keys = $keys;
     return $this;
   }
 
 
   /**
    * Filter results by read/unread status. Note that `true` means to return
    * only unread notifications, while `false` means to return only //read//
    * notifications. The default is `null`, which returns both.
    *
    * @param mixed True or false to filter results by read status. Null to remove
    *              the filter.
    * @return this
    * @task config
    */
   public function withUnread($unread) {
     $this->unread = $unread;
     return $this;
   }
 
 
 /* -(  Query Execution  )---------------------------------------------------- */
 
 
   protected function loadPage() {
     $story_table = new PhabricatorFeedStoryData();
     $notification_table = new PhabricatorFeedStoryNotification();
 
     $conn = $story_table->establishConnection('r');
 
     $data = queryfx_all(
       $conn,
       'SELECT story.*, notification.hasViewed FROM %R notification
          JOIN %R story ON notification.chronologicalKey = story.chronologicalKey
          %Q
          ORDER BY notification.chronologicalKey DESC
          %Q',
       $notification_table,
       $story_table,
       $this->buildWhereClause($conn),
       $this->buildLimitClause($conn));
 
-    $viewed_map = ipull($data, 'hasViewed', 'chronologicalKey');
+    // See T13623. Although most queries for notifications return unique
+    // stories, this isn't a guarantee.
+    $story_map = ipull($data, null, 'chronologicalKey');
 
     $stories = PhabricatorFeedStory::loadAllFromRows(
-      $data,
+      $story_map,
       $this->getViewer());
+    $stories = mpull($stories, null, 'getChronologicalKey');
 
-    foreach ($stories as $key => $story) {
-      $story->setHasViewed($viewed_map[$key]);
+    $results = array();
+    foreach ($data as $row) {
+      $story_key = $row['chronologicalKey'];
+      $has_viewed = $row['hasViewed'];
+
+      $results[] = id(clone $stories[$story_key])
+        ->setHasViewed($has_viewed);
     }
 
-    return $stories;
+    return $results;
   }
 
   protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
     $where = parent::buildWhereClauseParts($conn);
 
     if ($this->userPHIDs !== null) {
       $where[] = qsprintf(
         $conn,
         'notification.userPHID IN (%Ls)',
         $this->userPHIDs);
     }
 
     if ($this->unread !== null) {
       $where[] = qsprintf(
         $conn,
         'notification.hasViewed = %d',
         (int)!$this->unread);
     }
 
     if ($this->keys !== null) {
       $where[] = qsprintf(
         $conn,
         'notification.chronologicalKey IN (%Ls)',
         $this->keys);
     }
 
     return $where;
   }
 
   protected function willFilterPage(array $stories) {
     foreach ($stories as $key => $story) {
       if (!$story->isVisibleInNotifications()) {
         unset($stories[$key]);
       }
     }
 
     return $stories;
   }
 
   protected function getDefaultOrderVector() {
     return array('key');
   }
 
   public function getBuiltinOrders() {
     return array(
       'newest' => array(
         'vector' => array('key'),
         'name' => pht('Creation (Newest First)'),
         'aliases' => array('created'),
       ),
       'oldest' => array(
         'vector' => array('-key'),
         'name' => pht('Creation (Oldest First)'),
       ),
     );
   }
 
   public function getOrderableColumns() {
     return array(
       'key' => array(
         'table' => 'notification',
         'column' => 'chronologicalKey',
         'type' => 'string',
         'unique' => true,
       ),
     );
   }
 
   protected function applyExternalCursorConstraintsToQuery(
     PhabricatorCursorPagedPolicyAwareQuery $subquery,
     $cursor) {
-    $subquery->withKeys(array($cursor));
+
+    $subquery
+      ->withKeys(array($cursor))
+      ->setLimit(1);
+
   }
 
   protected function newExternalCursorStringForResult($object) {
     return $object->getChronologicalKey();
   }
 
   protected function newPagingMapFromPartialObject($object) {
     return array(
       'key' => $object->getChronologicalKey(),
     );
   }
 
   protected function getPrimaryTableAlias() {
     return 'notification';
   }
 
   public function getQueryApplicationClass() {
     return 'PhabricatorNotificationsApplication';
   }
 
 }