diff --git a/posthog/test/test_before_send.py b/posthog/test/test_before_send.py
index e2cda0a7..425294e6 100644
--- a/posthog/test/test_before_send.py
+++ b/posthog/test/test_before_send.py
@@ -16,6 +16,10 @@
 )
 
 
+_CIRCULAR: dict = {}
+_CIRCULAR["self"] = _CIRCULAR
+
+
 class TestClient(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
@@ -259,6 +263,8 @@ def test_before_send_callback_non_dict_output_drops_event(self):
                 "private-value",
                 ["malformed", "valid"],
             ),
+            # A value json cannot write costs only that event.
+            ("circular_reference", "private-key", _CIRCULAR, ["valid"]),
         ]
     )
     def test_malformed_before_send_event_does_not_stop_consumer_or_shutdown(