diff --git a/trytond/ir/sequence.py b/trytond/ir/sequence.py
index 28c28073ac..f3935cf443 100644
--- a/trytond/ir/sequence.py
+++ b/trytond/ir/sequence.py
@@ -20,7 +20,10 @@ class Sequence(OSV):
     _name = 'ir.sequence'
     _description = __doc__
     name = fields.Char('Sequence Name', required=True, translate=True)
-    code = fields.Selection('code_get', 'Sequence Type', required=True)
+    code = fields.Selection('code_get', 'Sequence Type', required=True,
+            states={
+                'readonly': "context.get('code')",
+            })
     active = fields.Boolean('Active')
     prefix = fields.Char('Prefix')
     suffix = fields.Char('Suffix')
@@ -50,6 +53,11 @@ class Sequence(OSV):
     def default_padding(self, cursor, user, context=None):
         return 0
 
+    def default_code(self, cursor, user, context=None):
+        if context is None:
+            context = {}
+        return context.get('code', False)
+
     def code_get(self, cursor, user, context=None):
         sequence_type_obj = self.pool.get('ir.sequence.type')
         sequence_type_ids = sequence_type_obj.search(cursor, user, [],
diff --git a/trytond/osv/orm.py b/trytond/osv/orm.py
index 5097561394..2ea2d3aa86 100644
--- a/trytond/osv/orm.py
+++ b/trytond/osv/orm.py
@@ -2683,14 +2683,16 @@ class ORM(object):
                                                 _symbol_set[0]] * len(arg[2]))))
                         if todel:
                             if arg[1] == 'in':
-                                qu1[-1] = '(' + qu1[-1] + ' or ' \
-                                        + arg[0] + ' is null)'
+                                qu1[-1] = '(' + qu1[-1] + ' OR ' \
+                                        '%s.%s IS NULL)' % \
+                                        (table._table, arg[0])
                             else:
-                                qu1[-1] = '(' + qu1[-1] + ' or ' \
-                                        + arg[0] + ' is not null)'
+                                qu1[-1] = '(' + qu1[-1] + ' OR ' \
+                                        '%s.%s IS NOT NULL)' % \
+                                        (table._table, arg[0])
                         qu2 += arg[2]
                     elif todel:
-                        qu1.append('(' + arg[0] + ' IS NULL)')
+                        qu1.append('(%s.%s IS NULL)' % (table._table, arg[0]))
                 else:
                     if arg[1] == 'in':
                         qu1.append(' false')