diff --git a/addons/point_of_sale/point_of_sale.py b/addons/point_of_sale/point_of_sale.py
index 9e0023f00c3..cd87117310c 100644
--- a/addons/point_of_sale/point_of_sale.py
+++ b/addons/point_of_sale/point_of_sale.py
@@ -973,11 +973,11 @@ class pos_order(osv.osv):
                 })
 
                 if data_type == 'product':
-                    key = ('product', values['partner_id'], values['product_id'])
+                    key = ('product', values['partner_id'], values['product_id'], values['debit'] > 0)
                 elif data_type == 'tax':
-                    key = ('tax', values['partner_id'], values['tax_code_id'],)
+                    key = ('tax', values['partner_id'], values['tax_code_id'], values['debit'] > 0)
                 elif data_type == 'counter_part':
-                    key = ('counter_part', values['partner_id'], values['account_id'])
+                    key = ('counter_part', values['partner_id'], values['account_id'], values['debit'] > 0)
                 else:
                     return