diff --git a/src/_zkapauthorizer/tests/test_storage_client.py b/src/_zkapauthorizer/tests/test_storage_client.py
index 611bc6127d252a4d28eceda6caa1c3faacfe4886..38a0e80bce19b2f041eaa45ba7425de393391674 100644
--- a/src/_zkapauthorizer/tests/test_storage_client.py
+++ b/src/_zkapauthorizer/tests/test_storage_client.py
@@ -341,8 +341,8 @@ class CallWithPassesTests(TestCase):
                 returned=Equals(accepted),
                 in_use=HasLength(0),
                 invalid=AfterPreprocessing(
-                    lambda invalid: invalid.keys(),
-                    Equals(rejected),
+                    lambda invalid: set(invalid.keys()),
+                    Equals(set(rejected)),
                 ),
                 spent=HasLength(0),
                 issued=Equals(set(accepted + rejected)),