diff --git a/codeforlife/user/serializers/user_test.py b/codeforlife/user/serializers/user_test.py
index fe41d48..c6d1407 100644
--- a/codeforlife/user/serializers/user_test.py
+++ b/codeforlife/user/serializers/user_test.py
@@ -31,7 +31,7 @@ def test_to_representation__teacher(self):
                 "student": None,
             },
             # TODO: remove in new schema.
-            non_model_fields=["requesting_to_join_class", "teacher", "student"],
+            non_model_fields={"requesting_to_join_class", "teacher", "student"},
         )
 
     def test_to_representation__student(self):
@@ -51,7 +51,7 @@ def test_to_representation__student(self):
                 },
             },
             # TODO: remove in new schema.
-            non_model_fields=["requesting_to_join_class", "teacher", "student"],
+            non_model_fields={"requesting_to_join_class", "teacher", "student"},
         )
 
     def test_to_representation__indy(self):