diff --git a/openff/bespokefit/tests/cli/test_worker.py b/openff/bespokefit/tests/cli/test_worker.py
index 69fdf1f2..e0a4bf98 100644
--- a/openff/bespokefit/tests/cli/test_worker.py
+++ b/openff/bespokefit/tests/cli/test_worker.py
@@ -17,7 +17,7 @@ def test_launch_worker(worker_type, runner, monkeypatch):
     in test_celery/test_spawn_worker
     """
 
-    def mock_spawn(*args):
+    def mock_spawn(*args, **kwargs):
         return True
 
     monkeypatch.setattr(celery, "_spawn_worker", mock_spawn)