diff --git a/gunicorn/workers/gtornado.py b/gunicorn/workers/gtornado.py
index 025de81b..544af7d0 100644
--- a/gunicorn/workers/gtornado.py
+++ b/gunicorn/workers/gtornado.py
@@ -134,7 +134,7 @@ class TornadoWorker(Worker):
 
                 def on_close(instance, server_conn):
                     self.handle_request()
-                    super(_HTTPServer, instance).on_close(server_conn)
+                    super().on_close(server_conn)
 
             server_class = _HTTPServer