diff --git a/asynctnt/instance.py b/asynctnt/instance.py
index badd94e..feb5c85 100644
--- a/asynctnt/instance.py
+++ b/asynctnt/instance.py
@@ -188,7 +188,9 @@ def _generate_root_folder_name(self):
     def get_random_port():
         sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         sock.bind(('', 0))
-        return sock.getsockname()[1]
+        port = sock.getsockname()[1]
+        sock.close()
+        return port
 
     def _create_initlua_template(self):
         return """