diff --git a/splitline.py b/splitline.py
index a3831c2..649c5f3 100644
--- a/splitline.py
+++ b/splitline.py
@@ -106,14 +106,14 @@ class SplitLine(ModelSQL, ModelView):
             'type': gettext('cashbook.msg_line_bookingtype_%s' % self.line.bookingtype),
             }
 
-    def get_amount_by_second_currency(self, to_currency):
+    def get_amount_by_second_currency(self, to_currency, amount=None):
         """ get amount, calculate credit/debit from currency of current
             cashbook to 'to_currency'
         """
         Currency = Pool().get('currency.currency')
 
         values = {
-            'amount': self.amount,
+            'amount': amount if amount is not None else self.amount,
             }
 
         if to_currency.id != self.line.cashbook.currency.id:
@@ -122,7 +122,7 @@ class SplitLine(ModelSQL, ModelView):
                 }):
                 values['amount'] = Currency.compute(
                         self.line.cashbook.currency,
-                        self.amount,
+                        values['amount'],
                         to_currency)
         return values