diff --git a/objets.py b/objets.py
index 2d52637..6867dc9 100644
--- a/objets.py
+++ b/objets.py
@@ -862,7 +862,7 @@ class InetOrgPerson(CransLdapObject):
 
 class proprio(CransLdapObject):
     u""" Un propriétaire de machine (adhérent, club…) """
-    __slots__ = ("_machines", "_factures", "full")
+    __slots__ = ("_machines", "_factures", "full", '_factures_last_update')
     can_be_by = {
         variables.created: [
             attributs.nounou,