diff --git management/univention-directory-manager-modules/modules/univention/admin/modules.py management/univention-directory-manager-modules/modules/univention/admin/modules.py
index 839cd52efa1..90ac0a0e4d3 100644
--- management/univention-directory-manager-modules/modules/univention/admin/modules.py
+++ management/univention-directory-manager-modules/modules/univention/admin/modules.py
@@ -206,7 +206,7 @@ def _get(module):
     """
     if not modules:
         update()
-    if isinstance(module, str):
+    if isinstance(module, six.string_types):
         return modules[module]
     return module