diff --git a/xep-0155.xml b/xep-0155.xml
index 11209cac..37ecfd08 100644
--- a/xep-0155.xml
+++ b/xep-0155.xml
@@ -29,7 +29,7 @@
     <version>0.9</version>
     <date>2006-10-05</date>
     <initials>ip</initials>
-    <remark><p>Added language field; replaced secure field with security field; changed otr field to list-single; several clarifications.</p></remark>
+    <remark><p>Added language field; replaced secure field with security field; changed otr field to list-single; not-acceptable error; several clarifications.</p></remark>
   </revision>
   <revision>
     <version>0.8</version>
@@ -262,7 +262,7 @@
          id='init1'>
   <thread>ffd7076498744578d10edabfe7f4a866</thread>
   <error code='501' type='cancel'>
-    <feature-not-implemented xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
+    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
     <text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>security</text>
   </error>
 </message>