diff --git a/xep-0158.xml b/xep-0158.xml
index a0073b21..f396cc70 100644
--- a/xep-0158.xml
+++ b/xep-0158.xml
@@ -460,7 +460,9 @@
   <p>A service that hosts multi-user chat rooms in accordance with <cite>XEP-0045</cite> MAY challenge unknown entities that seek to join such rooms or that send messages in such rooms.</p>
   <example caption='Sender Attempts to Join Chat Room'><![CDATA[
 <presence from='robot@abuser.com/zombie'
-          to='friendly-chat@muc.victim.com/robot101'/>
+          to='friendly-chat@muc.victim.com/robot101'>
+  <x xmlns='http://jabber.org/protocol/muc'/>
+</presence>
 ]]></example>
   <example caption='Challenger Offers a Choice of Challenges to Sender'><![CDATA[
 <message from='friendly-chat@muc.victim.com'