diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -6726,6 +6726,7 @@
       'PhabricatorProjectInterface',
       'PhabricatorDestructibleInterface',
       'PhabricatorSpacesInterface',
+      'PhabricatorMentionableInterface',
     ),
     'PholioMockCommentController' => 'PholioController',
     'PholioMockEditController' => 'PholioController',
diff --git a/src/applications/pholio/storage/PholioMock.php b/src/applications/pholio/storage/PholioMock.php
--- a/src/applications/pholio/storage/PholioMock.php
+++ b/src/applications/pholio/storage/PholioMock.php
@@ -10,7 +10,8 @@
     PhabricatorApplicationTransactionInterface,
     PhabricatorProjectInterface,
     PhabricatorDestructibleInterface,
-    PhabricatorSpacesInterface {
+    PhabricatorSpacesInterface,
+    PhabricatorMentionableInterface {
 
   const MARKUP_FIELD_DESCRIPTION  = 'markup:description';