diff --git modules/univention/office365/connector/connector.py modules/univention/office365/connector/connector.py
index 00de327..b80c1fd 100644
--- modules/univention/office365/connector/connector.py
+++ modules/univention/office365/connector/connector.py
@@ -574,7 +574,7 @@ class UserConnector(Connector):
 		"""
 		# TODO: use some kind of cache for the parsed objects (udm_object => parsed_object)
 		if not old_udm_user.should_sync() and new_udm_user.should_sync():
-			for alias in new_udm_user.aliases(new_udm_user.adconnection_aliases or self.default_adconnection):
+			for alias in new_udm_user.aliases(new_udm_user.adconnection_aliases or [self.default_adconnection]):
 				core = self.get_core(alias)
 				if not core:
 					continue