diff --git a/voucher.py b/voucher.py
index 4bb5b60..3800c24 100644
--- a/voucher.py
+++ b/voucher.py
@@ -480,7 +480,7 @@ class Voucher(Workflow, ModelSQL, ModelView):
             if line.move_line and line.amount != _ZERO:
                 to_reconcile[line] = [line.move_line]
 
-        amount = sum(ln['credit'] - ln['debit'] for ln in move_lines)
+        amount = abs(sum(ln['credit'] - ln['debit'] for ln in move_lines))
 
         if self.voucher_type == 'receipt':
             debit = amount