diff --git a/openerp/addons/base/tests/test_orm.py b/openerp/addons/base/tests/test_orm.py
index 6a387eec325..624dee5888c 100644
--- a/openerp/addons/base/tests/test_orm.py
+++ b/openerp/addons/base/tests/test_orm.py
@@ -166,6 +166,10 @@ class TestORM(common.TransactionCase):
                         ['date'], ['date:month', 'date:day'], lazy=False)
         self.assertEqual(len(rg), len(all_partners))
 
+    def test_write_duplicate(self):
+        cr, uid, p1 = self.cr, self.uid, self.p1
+        self.partner.write(cr, uid, [p1, p1], {'name': 'X'})
+
 
 class TestInherits(common.TransactionCase):
     """ test the behavior of the orm for models that use _inherits;
diff --git a/openerp/models.py b/openerp/models.py
index 7da181495a8..1fd2c7ae196 100644
--- a/openerp/models.py
+++ b/openerp/models.py
@@ -3896,7 +3896,7 @@ class BaseModel(object):
                 self._table, ','.join('"%s"=%s' % u[:2] for u in updates),
             )
             params = tuple(u[2] for u in updates if len(u) > 2)
-            for sub_ids in cr.split_for_in_conditions(ids):
+            for sub_ids in cr.split_for_in_conditions(set(ids)):
                 cr.execute(query, params + (sub_ids,))
                 if cr.rowcount != len(sub_ids):
                     raise MissingError(_('One of the records you are trying to modify has already been deleted (Document type: %s).') % self._description)