diff --git a/message.xml b/message.xml
new file mode 100644
index 0000000000..131b4f4b42
--- /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_location_already_assigned">
+            <field name="text">The location "%(location)s" has already been assigned by "%(assigned_by)s".</field>
+        </record>
+    </data>
+</tryton>
diff --git a/stock.py b/stock.py
index 2bf141cda0..315a199086 100644
--- a/stock.py
+++ b/stock.py
@@ -2,11 +2,14 @@
 # this repository contains the full copyright notices and license terms.
 import functools
 
+from trytond.i18n import gettext
 from trytond.model import ModelSQL, ModelView, Workflow, fields
 from trytond.pool import PoolMeta, Pool
 from trytond.pyson import Eval, If
 from trytond.transaction import Transaction
 
+from trytond.modules.stock.exceptions import AssignError
+
 __all__ = ['Location', 'ShipmentInternal', 'ShipmentInternal_Location',
     'ShipmentOut', 'ShipmentInReturn', 'Supply']
 
@@ -125,15 +128,6 @@ class ShipmentInternal(metaclass=PoolMeta):
             },
         depends=['state', 'from_location', 'to_location'])
 
-    @classmethod
-    def __setup__(cls):
-        super(ShipmentInternal, cls).__setup__()
-        cls._error_messages.update({
-                'location_already_assigned': (
-                    "The location '%(location)s' is already assigned "
-                    "by '%(assigned_by)s'."),
-                })
-
     @classmethod
     @ModelView.button
     @Workflow.transition('draft')
@@ -159,15 +153,17 @@ class ShipmentInternal(metaclass=PoolMeta):
                 if not location.assigned_by:
                     location.assigned_by = shipment
                     if location in locations:
-                        cls.raise_user_error(
-                            'location_already_assigned', {
+                        raise AssignError(
+                            gettext('stock_location_move'
+                                '.msg_location_already_assigned') % {
                                 'location': location.rec_name,
                                 'assigned_by': locations[location].rec_name,
                                 })
                     locations[location] = location.assigned_by
                 elif location.assigned_by != shipment:
-                    cls.raise_user_error(
-                        'location_already_assigned', {
+                    raise AssignError(
+                        gettext('stock_location_move'
+                            '.msg_location_already_assigned') % {
                             'location': location.rec_name,
                             'assigned_by': location.assigned_by.rec_name,
                             })
diff --git a/tests/scenario_stock_location_move.rst b/tests/scenario_stock_location_move.rst
index 054af32ae1..48ea6f37bd 100644
--- a/tests/scenario_stock_location_move.rst
+++ b/tests/scenario_stock_location_move.rst
@@ -70,7 +70,7 @@ Assign pallet from wrong location::
     >>> shipment.click('assign_try')  # doctest: +IGNORE_EXCEPTION_DETAIL
     Traceback (most recent call last):
         ...
-    UserError: ...
+    DomainValidationError: ...
 
 Concurrently move pallet::
 
@@ -91,7 +91,7 @@ Concurrently move pallet::
     >>> shipment2.click('assign_try')  # doctest: +IGNORE_EXCEPTION_DETAIL
     Traceback (most recent call last):
         ...
-    UserError: ...
+    AssignError: ...
 
     >>> shipment1.click('done')
 
diff --git a/tryton.cfg b/tryton.cfg
index edcbedd3c7..7832684579 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -7,3 +7,4 @@ extras_depend:
     stock_supply
 xml:
     stock.xml
+    message.xml