diff --git a/src/ifcblenderexport/io_export_ifc/ui.py b/src/ifcblenderexport/io_export_ifc/ui.py
index 77d8ae4dbc..3600253011 100644
--- a/src/ifcblenderexport/io_export_ifc/ui.py
+++ b/src/ifcblenderexport/io_export_ifc/ui.py
@@ -29,6 +29,7 @@ types_enum = []
 psetnames_enum = []
 psetfiles_enum = []
 classification_enum = []
+reference_enum = []
 attributes_enum = []
 documents_enum = []