diff --git a/tests/testserver/server.py b/tests/testserver/server.py
index 132221f7..c4587eef 100644
--- a/tests/testserver/server.py
+++ b/tests/testserver/server.py
@@ -78,7 +78,9 @@ class Server(threading.Thread):
     def _create_socket_and_bind(self):
         sock = socket.socket()
         sock.bind((self.host, self.port))
-        sock.listen(0)
+        # NB: when Python 2.7 is no longer supported, the argument
+        # can be removed to use a default backlog size
+        sock.listen(5)
         return sock
 
     def _close_server_sock_ignore_errors(self):