diff --git a/xep-0280.xml b/xep-0280.xml
index e7ab3dbf..b279666e 100644
--- a/xep-0280.xml
+++ b/xep-0280.xml
@@ -419,7 +419,7 @@
     <p>The following rules prevent some of the half-failure modes that have been an issue in other protocols:</p>
     <ul>
       <li>When a server attempts to deliver a (locally generated) carbon copy, and that carbon copy bounces with an error for any reason, the server MUST NOT forward that error back to the original sender.</li>
-      <li>The server can use the &lt;sent/&gt; or &lt;received/&gt; element in the bounce to determine that an error is from a carbon-copied message.</li>
+      <li>The server MUST NOT rely on the &lt;sent/&gt; or &lt;received/&gt; elements in the bounce to determine that an error is from a carbon-copied message, because entities are not required to include the original XML in their error replies as per <cite>RFC 6120</cite>, §8.3.1.</li>
     </ul>
   </section2>
   <section2 topic='Auto-responses' anchor='bizrules-autoresponses'>