diff --git a/xep-0166.xml b/xep-0166.xml
index dcf76b1a..12942951 100644
--- a/xep-0166.xml
+++ b/xep-0166.xml
@@ -946,7 +946,7 @@ PENDING  o----------------------+   |
       <p>The <strong>session-info</strong> action is used to send session-level information, such as (for Jingle RTP sessions) a ringing message.</p>
     </section3>
     <section3 topic='session-initiate' anchor='def-action-session-initiate'>
-      <p>The <strong>session-initiate</strong> action is used to request negotiation of a new Jingle session.</p>
+      <p>The <strong>session-initiate</strong> action is used to request negotiation of a new Jingle session. When sending a session-initiate, the value of the &CONTENT; element's 'disposition' attribute MUST be "session" (to be precise, if there are multiple &CONTENT; elements then at least one MUST have a disposition of "session"); if this rule is violated, the responder MUST return a &badrequest; error to the initiator.</p>
     </section3>
     <section3 topic='session-terminate' anchor='def-action-session-terminate'>
       <p>The <strong>session-terminate</strong> action is used to end an existing session.</p>