diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
--- a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
@@ -498,6 +498,12 @@
 
     if (!$this->canEvaluateFunction($function)) {
       if (!$allow_partial) {
+        // Allow PhabricatorApplicationSearchController to catch this exception
+        // and show a more helpful error message - https://we.phorge.it/T15704
+        if (get_class($this) === 'PhabricatorPeopleUserFunctionDatasource' &&
+            !$this->getViewer()->isLoggedIn()) {
+          return null;
+        }
         throw new PhabricatorTypeaheadInvalidTokenException(
           pht(
             'This datasource ("%s") can not evaluate the function "%s(...)".',