diff --git a/budget/forms.py b/budget/forms.py
index 7d6eb51..4b59a36 100644
--- a/budget/forms.py
+++ b/budget/forms.py
@@ -143,9 +143,7 @@ class BillForm(Form):
         self.payed_for.data = self.payed_for.default
 
     def validate_amount(self, field):
-        if field.data < 0:
-            field.data = abs(field.data)
-        elif field.data == 0:
+        if field.data == 0:
             raise ValidationError(_("Bills can't be null"))
 
 
diff --git a/budget/tests.py b/budget/tests.py
index 82465f9..eea7537 100644
--- a/budget/tests.py
+++ b/budget/tests.py
@@ -398,12 +398,10 @@ class BudgetTestCase(TestCase):
             'what': u'fromage à raclette',
             'payer': members_ids[0],
             'payed_for': members_ids,
-            # bill with a negative value should be converted to a positive
-            # value
             'amount': '-25'
         })
         bill = models.Bill.query.filter(models.Bill.date == '2011-08-12')[0]
-        self.assertEqual(bill.amount, 25)
+        self.assertEqual(bill.amount, -25)
 
         #add a bill with a comma
         self.app.post("/raclette/add", data={