diff --git a/src/web/fan/WebSocket.fan b/src/web/fan/WebSocket.fan
index bc4ad5ca2..1794ea60c 100644
--- a/src/web/fan/WebSocket.fan
+++ b/src/web/fan/WebSocket.fan
@@ -73,6 +73,7 @@ class WebSocket
     res.headers["Upgrade"] = "websocket"
     res.headers["Connection"] = "Upgrade"
     res.headers["Sec-WebSocket-Accept"] = secDigest(key)
+    res.headers.addNotNull("Sec-WebSocket-Protocol", req.headers["Sec-WebSocket-Protocol"])
 
     // take ownership of the underlying socket
     socket := res.upgrade(101)