diff --git a/openerp/addons/base/res/res_partner.py b/openerp/addons/base/res/res_partner.py
index 92414e764f3..ef22d935ffc 100644
--- a/openerp/addons/base/res/res_partner.py
+++ b/openerp/addons/base/res/res_partner.py
@@ -489,6 +489,17 @@ class res_partner(osv.osv, format_address):
     def write(self, cr, uid, ids, vals, context=None):
         if isinstance(ids, (int, long)):
             ids = [ids]
+        #res.partner must only allow to set the company_id of a partner if it
+        #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 vals.get('company_id'):
+            user_pool = self.pool.get('res.users')
+            for partner in self.browse(cr, uid, ids, context=context):
+                if partner.user_ids:
+                    user_companies = set([user.company_id.id for user 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 multiple 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)
diff --git a/openerp/addons/base/res/res_users.py b/openerp/addons/base/res/res_users.py
index 0e74a5379f4..b1aeaf28107 100644
--- a/openerp/addons/base/res/res_users.py
+++ b/openerp/addons/base/res/res_users.py
@@ -279,6 +279,13 @@ class res_users(osv.osv):
 
         return result
 
+    def create(self, cr, uid, vals, context=None):
+        user_id = super(res_users, self).create(cr, uid, vals, context=context)
+        user = self.browse(cr, uid, user_id, context=context)
+        if user.partner_id.company_id: 
+            user.partner_id.write({'company_id': user.company_id.id})
+        return user_id
+
     def write(self, cr, uid, ids, values, context=None):
         if not hasattr(ids, '__iter__'):
             ids = [ids]
@@ -293,7 +300,11 @@ class res_users(osv.osv):
                 uid = 1 # safe fields only, so we write as super-user to bypass access rights
 
         res = super(res_users, self).write(cr, uid, ids, values, context=context)
-
+        if 'company_id' in values:
+            for user in self.browse(cr, uid, ids, context=context):
+                # if partner is global we keep it that way
+                if user.partner_id.company_id and user.partner_id.company_id.id != values['company_id']: 
+                    user.partner_id.write({'company_id': user.company_id.id})
         # clear caches linked to the users
         self.pool.get('ir.model.access').call_cache_clearing_methods(cr)
         clear = partial(self.pool.get('ir.rule').clear_cache, cr)