diff --git a/addons/account/invoice.py b/addons/account/invoice.py
index 611ebf7fe84..e7d92587b3d 100644
--- a/addons/account/invoice.py
+++ b/addons/account/invoice.py
@@ -1022,14 +1022,14 @@ class account_invoice_tax(osv.osv):
                 if inv.type in ('out_invoice','in_invoice'):
                     val['base_code_id'] = tax['base_code_id']
                     val['tax_code_id'] = tax['tax_code_id']
-                    val['base_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['base'] * tax['base_sign'], context={'date': inv.date_invoice})
-                    val['tax_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['amount'] * tax['tax_sign'], context={'date': inv.date_invoice})
+                    val['base_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['base'] * tax['base_sign'], context={'date': inv.date_invoice or time.strftime('%Y-%m-%d')})
+                    val['tax_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['amount'] * tax['tax_sign'], context={'date': inv.date_invoice or time.strftime('%Y-%m-%d')})
                     val['account_id'] = tax['account_collected_id'] or line.account_id.id
                 else:
                     val['base_code_id'] = tax['ref_base_code_id']
                     val['tax_code_id'] = tax['ref_tax_code_id']
-                    val['base_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['base'] * tax['ref_base_sign'], context={'date': inv.date_invoice})
-                    val['tax_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['amount'] * tax['ref_tax_sign'], context={'date': inv.date_invoice})
+                    val['base_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['base'] * tax['ref_base_sign'], context={'date': inv.date_invoice or time.strftime('%Y-%m-%d')})
+                    val['tax_amount'] = cur_obj.compute(cr, uid, inv.currency_id.id, company_currency, val['amount'] * tax['ref_tax_sign'], context={'date': inv.date_invoice or time.strftime('%Y-%m-%d')})
                     val['account_id'] = tax['account_paid_id'] or line.account_id.id
 
                 key = (val['tax_code_id'], val['base_code_id'], val['account_id'])