diff --git a/addons/point_of_sale/pos.py b/addons/point_of_sale/pos.py
index 9a02a95dc7b..a4c3cd9474d 100644
--- a/addons/point_of_sale/pos.py
+++ b/addons/point_of_sale/pos.py
@@ -1155,12 +1155,10 @@ class pos_order_line(osv.osv):
         else :
             return {'value': {'notice':'No Discount', 'price_ded':price*discount*0.01 or 0.0}}
         
-    def onchange_qty(self, cr, uid, ids, price_subtotal_incl, discount, qty, price, context=None):
-        price_sub = price_subtotal_incl
+    def onchange_qty(self, cr, uid, ids, discount, qty, price, context=None):
+        subtotal = qty * price
         if discount:
-            subtotal = price_sub-(price_subtotal_incl*(discount*0.01))
-        else:
-            subtotal = qty * price
+            subtotal = subtotal - (subtotal * discount / 100)
         return {'value': {'price_subtotal_incl': subtotal}}
     
     _columns = {
diff --git a/addons/point_of_sale/pos_view.xml b/addons/point_of_sale/pos_view.xml
index 172b1231d97..2cd0a02c55e 100644
--- a/addons/point_of_sale/pos_view.xml
+++ b/addons/point_of_sale/pos_view.xml
@@ -22,7 +22,7 @@
                             <field name="lines" colspan="4" nolabel="1">
                                 <tree string="Order lines" editable="bottom">
                                     <field name="product_id" on_change="onchange_product_id(parent.pricelist_id,product_id,qty,parent.partner_id)" width="275" />
-                                    <field name="qty" on_change="onchange_qty(price_subtotal_incl, discount, qty, price_unit)"/>
+                                    <field name="qty" on_change="onchange_qty(discount, qty, price_unit)"/>
                                     <!--<field name="qty" on_change="onchange_qty(qty,price_unit)"/>-->
                                     <!--field name="qty_rfd" groups="base.group_extended"/-->
                                     <field name="price_ded" on_change="onchange_ded(price_ded, price_subtotal_incl,price_unit)" invisible="1"/>