diff --git a/locale/es.po b/locale/es.po
index 524e198..7d2f8a8 100644
--- a/locale/es.po
+++ b/locale/es.po
@@ -2,7 +2,7 @@
 msgid ""
 msgstr "Content-Type: text/plain; charset=utf-8\n"
 
-msgctxt "error:stock.product.category.location:"
+msgctxt "model:ir.message,text:msg_category_location_unique_key"
 msgid "Category and location must be unique."
 msgstr "Categoria y ubicación deben ser únicos."
 
diff --git a/location.py b/location.py
index f2e4a96..b3e9249 100644
--- a/location.py
+++ b/location.py
@@ -4,6 +4,8 @@ from trytond.model import ModelView, ModelSQL, fields
 from trytond.pyson import Eval, Bool, Not, Equal
 from trytond.pool import PoolMeta, Pool
 from trytond.transaction import Transaction
+from trytond.exceptions import UserError
+from trytond.i18n import gettext
 from sql.aggregate import Max
 
 
@@ -34,16 +36,11 @@ class ProductCategoryLocation(ModelSQL, ModelView):
         ], depends=['warehouse'])
     sequence = fields.Integer('Sequence')
 
-    @classmethod
-    def __setup__(cls):
-        super(ProductCategoryLocation, cls).__setup__()
-        cls._error_messages.update({
-            'unique_key': 'Category and location must be unique.'})
-
     @staticmethod
     def _compute_sequence_where(table, record):
-        return ((table.category == record['category']) &
-            (table.warehouse == record['warehouse']))
+        return (
+            (table.category == record['category'])
+            & (table.warehouse == record['warehouse']))
 
     @staticmethod
     def _compute_sequence(table, record):
@@ -63,7 +60,7 @@ class ProductCategoryLocation(ModelSQL, ModelView):
             if not values.get('sequence', None):
                 values['sequence'] = cls._compute_sequence(
                     cls.__table__(), values)
-        return super(ProductCategoryLocation, cls).create(vlist)
+        return super().create(vlist)
 
     @classmethod
     def default_warehouse(cls):
@@ -88,16 +85,20 @@ class ProductCategoryLocation(ModelSQL, ModelView):
         for record in records:
             _uq = record._get_unique_key()
             if values.get(_uq):
-                cls.raise_user_error('unique_key')
+                raise UserError(gettext(
+                    'stock_product_category_location.'
+                    'msg_category_location_unique_key'))
             values.setdefault(_uq, 1)
 
         others = cls.search([('id', 'not in', list(map(int, records)))])
         for other in others:
             _uq = other._get_unique_key()
             if values.get(_uq):
-                cls.raise_user_error('unique_key')
+                raise UserError(gettext(
+                    'stock_product_category_location.'
+                    'msg_category_location_unique_key'))
 
-        super(ProductCategoryLocation, cls).validate(records)
+        super().validate(records)
 
 
 class Location(metaclass=PoolMeta):
@@ -118,6 +119,6 @@ class Location(metaclass=PoolMeta):
 
     @classmethod
     def view_attributes(cls):
-        return super(Location, cls).view_attributes() + [
+        return super().view_attributes() + [
             ('//page[@id="categories"]', 'states', {
                 'invisible': ~Eval('type').in_(['warehouse', 'storage'])})]
diff --git a/message.xml b/message.xml
new file mode 100644
index 0000000..57ead0a
--- /dev/null
+++ b/message.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0"?>
+<!-- The COPYRIGHT file at the top level of this repository contains the full
+     copyright notices and license terms. -->
+<tryton>
+    <data grouped="1">
+		<!-- stock.product.category.location -->
+        <record model="ir.message" id="msg_category_location_unique_key">
+            <field name="text">Category and location must be unique.</field>
+        </record>
+    </data>
+</tryton>
diff --git a/stock.py b/stock.py
index 7b505ba..143dac2 100644
--- a/stock.py
+++ b/stock.py
@@ -9,7 +9,7 @@ class ShipmentOut(metaclass=PoolMeta):
     __name__ = 'stock.shipment.out'
 
     def _get_inventory_move(self, move):
-        res = super(ShipmentOut, self)._get_inventory_move(move)
+        res = super()._get_inventory_move(move)
         if not res or hasattr(res, 'unit_load'):
             return res
         for c in res.product.categories:
@@ -27,14 +27,13 @@ class ShipmentOut(metaclass=PoolMeta):
 class ShipmentOutReturn(metaclass=PoolMeta):
     __name__ = 'stock.shipment.out.return'
 
-    @classmethod
-    def _get_inventory_moves(cls, incoming_move):
-        res = super(ShipmentOutReturn, cls)._get_inventory_moves(incoming_move)
+    def _get_inventory_move(self, incoming_move):
+        res = super()._get_inventory_move(incoming_move)
         if not res:
             return res
         for c in res.product.categories:
             _to_location = c.get_default_location(
-                **cls._get_default_location_params(incoming_move))
+                **self._get_default_location_params(incoming_move))
             if _to_location:
                 res.to_location = _to_location
                 break
@@ -48,14 +47,13 @@ class ShipmentOutReturn(metaclass=PoolMeta):
 class ShipmentIn(metaclass=PoolMeta):
     __name__ = 'stock.shipment.in'
 
-    @classmethod
-    def _get_inventory_moves(cls, incoming_move):
-        res = super(ShipmentIn, cls)._get_inventory_moves(incoming_move)
+    def _get_inventory_move(self, incoming_move):
+        res = super()._get_inventory_move(incoming_move)
         if not res:
             return res
         for c in res.product.categories:
             _to_location = c.get_default_location(
-                **cls._get_default_location_params(incoming_move))
+                **self._get_default_location_params(incoming_move))
             if _to_location:
                 res.to_location = _to_location
                 break
diff --git a/tryton.cfg b/tryton.cfg
index 9620bee..06b63a1 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -11,3 +11,4 @@ extras_depend:
 xml:
   location.xml
   product.xml
+  message.xml
\ No newline at end of file