diff --git a/lib/kolab_api_service.php b/lib/kolab_api_service.php
--- a/lib/kolab_api_service.php
+++ b/lib/kolab_api_service.php
@@ -179,7 +179,7 @@
 
                     $value = implode('', $value);
                 } else if (is_string($value)) {
-                    $value = $this->conf->expand($_value, $custom = Array('base_dn' => $this->base_dn()));
+                    $value = $this->conf->expand($value, $custom = Array('base_dn' => $this->base_dn()));
                 }
 
                 if (is_array($v)) {