The `upload_to` hack is no longer needed on Django 1.7+

private_storage/fields.py

 #-*- coding: utf-8 -*-
 from __future__ import unicode_literals
 import os
+
+import django
 from django.core.exceptions import ValidationError
 from django.core.files.uploadedfile import UploadedFile
 from django.db import models
@@ -30,7 +32,7 @@ class PrivateFileField(models.FileField):
         self.max_file_size = kwargs.pop("max_file_size", None)
 
         kwargs.setdefault('storage', private_storage)
-        if self._upload:
+        if self._upload and django.VERSION < (1,7):
             kwargs.setdefault('upload_to', 'uploads')  # shut up warnings from Django 1.6- model validation
         super(PrivateFileField, self).__init__(*args, **kwargs)