diff --git a/t/unit/asynchronous/test_hub.py b/t/unit/asynchronous/test_hub.py
index e46d338df..97551dd1d 100644
--- a/t/unit/asynchronous/test_hub.py
+++ b/t/unit/asynchronous/test_hub.py
@@ -568,4 +568,4 @@ def test__pop_ready_pops_ready_items(self):
     def test__pop_ready_uses_lock(self):
         with patch.object(self.hub, '_ready_lock', autospec=True) as lock:
             self.hub._pop_ready()
-            assert lock.__enter__.called_once()
+            lock.__enter__.assert_called_once()