diff --git a/accountant/api/views/models.py b/accountant/api/views/models.py
index 661e81d..7df9f51 100644
--- a/accountant/api/views/models.py
+++ b/accountant/api/views/models.py
@@ -138,7 +138,7 @@ operation_model = api.model('Operation', {
         description='Canceled status of the operation (for a scheduled one)')
 })
 
-operation_with_sold_model = api.extend(
+operation_with_sold_model = api.inherit(
     'OperationWithSold', operation_model, {
         'sold': fields.Float(
             readonly=True,