diff --git a/tests/unit_server/arghandler_test.py b/tests/unit_server/arghandler_test.py
index be2d5022..9cf69f5f 100644
--- a/tests/unit_server/arghandler_test.py
+++ b/tests/unit_server/arghandler_test.py
@@ -669,7 +669,7 @@ def _error_it(_: Any):
         print(arg)
         arghand.add_argument(
             arg,
-            type=lambda x: _error_it(x),
+            type=_error_it,
         )
 
     with pytest.raises(tornado.web.HTTPError) as e: