diff --git a/budget/forms.py b/budget/forms.py
index 8db90be..f5c3fb5 100644
--- a/budget/forms.py
+++ b/budget/forms.py
@@ -48,7 +48,8 @@ def get_billform_for(project, set_default=True, **kwargs):
 class CommaDecimalField(DecimalField):
     """A class to deal with comma in Decimal Field"""
     def process_formdata(self, value):
-        value[0] = str(value[0]).replace(',', '.')
+        if value:
+            value[0] = str(value[0]).replace(',', '.')
         return super(CommaDecimalField, self).process_formdata(value)