diff --git a/exceptions.py b/exceptions.py
new file mode 100644
index 0000000000..ed877fb1b8
--- /dev/null
+++ b/exceptions.py
@@ -0,0 +1,7 @@
+# This file is part of Tryton.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+from trytond.model.exceptions import ValidationError
+
+
+class DuplicateError(ValidationError):
+    pass
diff --git a/message.xml b/message.xml
new file mode 100644
index 0000000000..c7e4741e03
--- /dev/null
+++ b/message.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0"?>
+<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
+this repository contains the full copyright notices and license terms. -->
+<tryton>
+    <data group="1">
+        <record model="ir.message" id="msg_duplicate_numbers">
+            <field name="text">The coupons numbered "%(numbers)s" are duplicated.</field>
+        </record>
+    </data>
+</tryton>
diff --git a/sale.py b/sale.py
index e9aacd8377..f584705320 100644
--- a/sale.py
+++ b/sale.py
@@ -4,6 +4,7 @@ from sql import Literal
 from sql.aggregate import Count
 from sql.conditionals import Case, Coalesce
 
+from trytond.i18n import gettext
 from trytond.model import (
     ModelSQL, ModelView, Workflow, fields, DeactivableMixin)
 from trytond.pool import PoolMeta, Pool
@@ -11,6 +12,8 @@ from trytond.pyson import Eval
 from trytond.tools import grouped_slice, reduce_ids
 from trytond.transaction import Transaction
 
+from .exceptions import DuplicateError
+
 __all__ = ['Promotion', 'PromotionCoupon', 'PromotionCouponNumber']
 
 
@@ -70,10 +73,6 @@ class PromotionCouponNumber(DeactivableMixin, ModelSQL, ModelView):
     @classmethod
     def __setup__(cls):
         super(PromotionCouponNumber, cls).__setup__()
-        cls._error_messages.update({
-                'duplicate_numbers': (
-                    "The coupon numbered '%(numbers)s' are duplicated."),
-                })
         cls.active = fields.Function(
             fields.Boolean("Active"), 'get_active', searcher='search_active')
 
@@ -189,9 +188,9 @@ class PromotionCouponNumber(DeactivableMixin, ModelSQL, ModelView):
             numbers = ', '.join(n.number for n in duplicates[:5])
             if len(duplicates) > 5:
                 numbers += '...'
-            cls.raise_user_error('duplicate_numbers', {
-                    'numbers': numbers,
-                    })
+            raise DuplicateError(
+                gettext('sale_promotion_coupon.msg_duplicate_numbers',
+                    numbers=numbers))
 
 
 class Sale(metaclass=PoolMeta):
diff --git a/tryton.cfg b/tryton.cfg
index 010f88c194..2c6e630d35 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -6,3 +6,4 @@ depends:
     sale_promotion
 xml:
     sale.xml
+    message.xml