diff --git a/addons/account/account.py b/addons/account/account.py
index 282233276c6..0c1bfa62409 100644
--- a/addons/account/account.py
+++ b/addons/account/account.py
@@ -1701,6 +1701,11 @@ class account_tax(osv.osv):
         ids = self.search(cr, user, args, limit=limit, context=context)
         return self.name_get(cr, user, ids, context=context)
 
+    def write(self, cr, uid, ids, vals, context=None):
+        if vals.get('type', False) and vals['type'] in ('none', 'code'):
+            vals.update({'amount': 0.0})
+        return super(account_tax, self).write(cr, uid, ids, vals, context=context)
+
     def search(self, cr, uid, args, offset=0, limit=None, order=None, context=None, count=False):
         journal_pool = self.pool.get('account.journal')
 
diff --git a/addons/account/account_view.xml b/addons/account/account_view.xml
index bfe32537708..6d3f63118e1 100644
--- a/addons/account/account_view.xml
+++ b/addons/account/account_view.xml
@@ -849,7 +849,7 @@
                     <notebook colspan="4">
                         <page string="Tax Definition">
                             <field name="applicable_type"/>
-                            <field name="amount" attrs="{'readonly':[('type','=','none'),('type','=','code')]}"/>
+                            <field name="amount" attrs="{'readonly':[('type','in',('none', 'code'))]}"/>
                             <field groups="base.group_extended" name="include_base_amount"/>
                             <field groups="base.group_extended" name="domain"/>
                             <newline/>