diff --git a/openerp/addons/base/res/res_partner.py b/openerp/addons/base/res/res_partner.py
index 97725313c4c..f28e54d6f15 100644
--- a/openerp/addons/base/res/res_partner.py
+++ b/openerp/addons/base/res/res_partner.py
@@ -493,13 +493,12 @@ class res_partner(osv.osv, format_address):
         #is the same as the company of all users that inherit from this partner
         #(this is to allow the code from res_users to write to the partner!) or
         #if setting the company_id to False (this is compatible with any user company)
-        if 'company_id' in vals and vals.get('company_id'):
+        if vals.get('company_id'):
             user_pool = self.pool.get('res.users')
-            for partner in ids:
-                uspa = user_pool.search(cr, uid, [('partner_id', '=', partner)], context=context)
-                usco = set([user.company_id.id for user in user_pool.browse(cr, uid, uspa, context=context)])
-                if usco and len(usco) > 1:
-                    raise osv.except_osv(_("Warning"),_("You can not chnage the partner company as the partner has mutiple user linked with different companies."))
+            for partner in self.browse(cr, uid, ids, context=context):
+                user_companies = set([users.company_id.id for users in partner.user_ids])
+                if len(user_companies) > 1 or vals.get('company_id') not in user_companies:
+                    raise osv.except_osv(_("Warning"),_("You can not change the company as the partner/user has mutiple user linked with different companies."))
         result = super(res_partner,self).write(cr, uid, ids, vals, context=context)
         for partner in self.browse(cr, uid, ids, context=context):
             self._fields_sync(cr, uid, partner, vals, context)