diff --git a/passerelle_imio_extra_fees/models.py b/passerelle_imio_extra_fees/models.py
index 6fb472f..a63582f 100644
--- a/passerelle_imio_extra_fees/models.py
+++ b/passerelle_imio_extra_fees/models.py
@@ -67,13 +67,13 @@ class ExtraFees(BaseResource):
                 destination = basket_item["request_data"]["form_var_destinations_raw"]
                 if destination and "mail" in destination:
                     postage_fee = 0
-                postage_fee = nb_letter * postage_fee
                 if Decimal(basket_item['request_data']['postage_fee']) > postage_fee:
                     postage_fee = Decimal(basket_item['request_data']['postage_fee'])
             except KeyError:
                 # basket item not associated with any document, no fee
                 pass
         nb_letter = int(nb_documents / int(self.max_doc_in_letter)) + (((nb_documents % int(self.max_doc_in_letter)) > 0) and 1 or 0)
+        postage_fee = nb_letter * postage_fee
         return {'data': [{'subject': force_text(_('Postage')), 'amount': str(postage_fee)}]}
 
     def namur_compute(self, request, **kwargs):