diff --git a/tests/test_serialization.py b/tests/test_serialization.py
index 76d5391..cd7b6d7 100644
--- a/tests/test_serialization.py
+++ b/tests/test_serialization.py
@@ -10,4 +10,4 @@ from .utils import create_photo, pickleback
 def test_imagespecfield():
     instance = create_photo('pickletest2.jpg')
     thumbnail = pickleback(instance.thumbnail)
-    thumbnail.source_file
+    thumbnail.generate()