diff --git a/README.md b/README.md
index bba1c099b..7e0c0fb24 100644
--- a/README.md
+++ b/README.md
@@ -199,6 +199,7 @@ to a single process.
         consider the connection closed (`60000`)
       - `pingInterval` (`Number`): how many ms before sending a new ping
         packet (`25000`)
+      - `upgradeTimeout` (`Number`): how many ms before an uncompleted transport upgrade is cancelled (`10000`)
       - `maxHttpBufferSize` (`Number`): how many bytes or characters a message
         can be when polling, before closing the session (to avoid DoS). Default
         value is `10E7`.