diff --git a/openerp/osv/orm.py b/openerp/osv/orm.py
index 6ac65125620..62ff24a2a3c 100644
--- a/openerp/osv/orm.py
+++ b/openerp/osv/orm.py
@@ -2716,10 +2716,7 @@ class BaseModel(object):
                                 ('float8', 'float', get_pg_type(f)[1], '::'+get_pg_type(f)[1]),
                             ]
                             if f_pg_type == 'varchar' and f._type == 'char' and ((f.size is None and f_pg_size) or f_pg_size < f.size):
-                                cr.execute('ALTER TABLE "%s" RENAME COLUMN "%s" TO temp_change_size' % (self._table, k))
-                                cr.execute('ALTER TABLE "%s" ADD COLUMN "%s" %s' % (self._table, k, pg_varchar(f.size)))
-                                cr.execute('UPDATE "%s" SET "%s"=temp_change_size::%s' % (self._table, k, pg_varchar(f.size)))
-                                cr.execute('ALTER TABLE "%s" DROP COLUMN temp_change_size CASCADE' % (self._table,))
+                                cr.execute('ALTER TABLE "%s" ALTER COLUMN "%s" TYPE %s' % (self._table, k, pg_varchar(f.size)))
                                 cr.commit()
                                 _schema.debug("Table '%s': column '%s' (type varchar) changed size from %s to %s",
                                     self._table, k, f_pg_size or 'unlimited', f.size or 'unlimited')
@@ -2727,10 +2724,10 @@ class BaseModel(object):
                                 if (f_pg_type==c[0]) and (f._type==c[1]):
                                     if f_pg_type != f_obj_type:
                                         ok = True
-                                        cr.execute('ALTER TABLE "%s" RENAME COLUMN "%s" TO temp_change_size' % (self._table, k))
+                                        cr.execute('ALTER TABLE "%s" RENAME COLUMN "%s" TO __temp_type_cast' % (self._table, k))
                                         cr.execute('ALTER TABLE "%s" ADD COLUMN "%s" %s' % (self._table, k, c[2]))
-                                        cr.execute(('UPDATE "%s" SET "%s"=temp_change_size'+c[3]) % (self._table, k))
-                                        cr.execute('ALTER TABLE "%s" DROP COLUMN temp_change_size CASCADE' % (self._table,))
+                                        cr.execute(('UPDATE "%s" SET "%s"= __temp_type_cast'+c[3]) % (self._table, k))
+                                        cr.execute('ALTER TABLE "%s" DROP COLUMN  __temp_type_cast CASCADE' % (self._table,))
                                         cr.commit()
                                         _schema.debug("Table '%s': column '%s' changed type from %s to %s",
                                             self._table, k, c[0], c[1])