diff --git a/addons/purchase/stock.py b/addons/purchase/stock.py
index a966ac8308f..12a18984361 100644
--- a/addons/purchase/stock.py
+++ b/addons/purchase/stock.py
@@ -83,6 +83,14 @@ class stock_move(osv.osv):
 class stock_picking(osv.osv):
     _inherit = 'stock.picking'
 
+    def _get_partner_to_invoice(self, cr, uid, picking, context=None):
+        """ Inherit the original function of the 'stock' module
+            We select the partner of the purchase order as the partner of the invoice
+        """
+        if picking.move_lines and picking.move_lines[0] and picking.move_lines[0].purchase_line_id:
+            return picking.move_lines[0].purchase_line_id.order_id.partner_id and picking.move_lines[0].purchase_line_id.order_id.partner_id.id
+        return super(stock_picking, self)._get_partner_to_invoice(cr, uid, picking, context=context)
+    
     def _get_to_invoice(self, cr, uid, ids, name, args, context=None):
         res = {}
         for picking in self.browse(cr, uid, ids, context=context):
diff --git a/addons/sale_stock/sale_stock.py b/addons/sale_stock/sale_stock.py
index 9e409f8be31..f2c6f529dcc 100644
--- a/addons/sale_stock/sale_stock.py
+++ b/addons/sale_stock/sale_stock.py
@@ -396,6 +396,17 @@ class stock_location_route(osv.osv):
 class stock_picking(osv.osv):
     _inherit = "stock.picking"
 
+    def _get_partner_to_invoice(self, cr, uid, picking, context=None):
+        """ Inherit the original function of the 'stock' module
+            We select the partner of the sales order as the partner of the customer invoice
+        """
+        saleorder_ids = self.pool['sale.order'].search(cr, uid, [('procurement_group_id' ,'=', picking.group_id.id)], context=context)
+        saleorders = self.pool['sale.order'].browse(cr, uid, saleorder_ids, context=context)
+        if saleorders and saleorders[0]:
+            saleorder = saleorders[0]
+            return saleorder.partner_invoice_id.id
+        return super(stock_picking, self)._get_partner_to_invoice(cr, uid, picking, context=context)
+    
     def _get_sale_id(self, cr, uid, ids, name, args, context=None):
         sale_obj = self.pool.get("sale.order")
         res = {}
diff --git a/addons/stock_account/stock.py b/addons/stock_account/stock.py
index 05f0fe3f6ce..e6a26bd9d64 100644
--- a/addons/stock_account/stock.py
+++ b/addons/stock_account/stock.py
@@ -190,6 +190,14 @@ class stock_picking(osv.osv):
         invoice_obj = self.pool.get('account.invoice')
         return invoice_obj.create(cr, uid, vals, context=context)
 
+    def _get_partner_to_invoice(self, cr, uid, picking, context=None):
+        """ Gets the partner that will be invoiced
+            Note that this function is inherited in the sale and purchase modules
+            @param picking: object of the picking for which we are selecting the partner to invoice
+            @return: object of the partner to invoice
+        """
+        return picking.partner_id and picking.partner_id.id
+        
     def action_invoice_create(self, cr, uid, ids, journal_id, group=False, type='out_invoice', context=None):
         """ Creates invoice based on the invoice state selected for picking.
         @param journal_id: Id of journal
@@ -197,20 +205,14 @@ class stock_picking(osv.osv):
         @param type: Type invoice to be created
         @return: Ids of created invoices for the pickings
         """
-        saleorder_model = self.pool['sale.order']
         context = context or {}
         todo = {}
 
         for picking in self.browse(cr, uid, ids, context=context):
+            partner = self._get_partner_to_invoice(cr, uid, picking, context)
             #grouping is based on the invoiced partner
             if group:
-                saleorder_ids = saleorder_model.search(cr, uid, [('procurement_group_id' ,'=', picking.group_id.id)], context=context)
-                saleorders = saleorder_model.browse(cr, uid, saleorder_ids, context=context)
-                if saleorders and saleorders[0]:
-                    saleorder = saleorders[0]
-                    key = "%s" % saleorder.partner_invoice_id.id
-                else:
-                    key = "Pick %s" % picking.id
+                key = partner
             else:
                 key = picking.id
             for move in picking.move_lines: