diff --git a/plugins/ktcore/admin/documentFields.php b/plugins/ktcore/admin/documentFields.php
index a8ea826..afa9aa5 100755
--- a/plugins/ktcore/admin/documentFields.php
+++ b/plugins/ktcore/admin/documentFields.php
@@ -9,6 +9,7 @@ require_once(KT_LIB_DIR . '/metadata/fieldset.inc.php');
 require_once(KT_LIB_DIR . '/metadata/metadatautil.inc.php');
 
 require_once(KT_LIB_DIR . '/widgets/fieldWidgets.php');
+require_once(KT_LIB_DIR . '/documentmanagement/MDTree.inc');
 
 
 // FIXME shouldn't this inherit from AdminDispatcher?