diff --git a/carrier.py b/carrier.py
index 985f508..12495d7 100644
--- a/carrier.py
+++ b/carrier.py
@@ -4,7 +4,6 @@
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.pool import Pool, PoolMeta
 
-__metaclass__ = PoolMeta
 __all__ = ['CarrierZip', 'Carrier']
 
 
@@ -38,6 +37,7 @@ class CarrierZip(ModelSQL, ModelView):
 
 
 class Carrier:
+    __metaclass__ = PoolMeta
     __name__ = 'carrier'
     zips = fields.One2Many('carrier.zip', 'carrier', 'Carrier Zips')
 
diff --git a/sale.py b/sale.py
index d1e8a9e..c6ef3bc 100644
--- a/sale.py
+++ b/sale.py
@@ -7,10 +7,10 @@ from trytond.pyson import Eval
 from trytond.transaction import Transaction
 
 __all__ = ['Sale']
-__metaclass__ = PoolMeta
 
 
 class Sale:
+    __metaclass__ = PoolMeta
     __name__ = 'sale.sale'
     carrier_domain = fields.Function(fields.One2Many('carrier', None,
             'Carrier Domain', depends=['shipment_address', 'party']),