diff --git a/addons/account_voucher/account_voucher.py b/addons/account_voucher/account_voucher.py
index 1287c7b3c18..223705af85e 100644
--- a/addons/account_voucher/account_voucher.py
+++ b/addons/account_voucher/account_voucher.py
@@ -1106,7 +1106,8 @@ class account_voucher(osv.osv):
                         # otherwise we use the rates of the system (giving the voucher date in the context)
                         amount_currency = currency_obj.compute(cr, uid, company_currency, line.move_line_id.currency_id.id, move_line['debit']-move_line['credit'], context=ctx)
                 if line.amount == line.amount_unreconciled and line.move_line_id.currency_id.id == voucher_currency:
-                    foreign_currency_diff = line.move_line_id.amount_residual_currency + amount_currency
+                    sign = voucher_brw.type in ('payment', 'purchase') and -1 or 1
+                    foreign_currency_diff = sign * line.move_line_id.amount_residual_currency + amount_currency
 
             move_line['amount_currency'] = amount_currency
             voucher_line = move_line_obj.create(cr, uid, move_line)