diff --git a/xep.ent b/xep.ent
index bca67a21..5713c0a8 100644
--- a/xep.ent
+++ b/xep.ent
@@ -477,6 +477,7 @@ THE SOFTWARE.
 <!ENTITY rfc3264 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3264'>RFC 3264</link></span> <note>RFC 3264: An Offer/Answer Model with the Session Description Protocol (SDP) &lt;<link url='http://tools.ietf.org/html/rfc3264'>http://tools.ietf.org/html/rfc3264</link>&gt;.</note>" >
 <!ENTITY rfc3269 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3269'>RFC 3269</link></span> <note>RFC 3269: UTF-8, a transformation format of ISO 10646 &lt;<link url='http://tools.ietf.org/html/rfc3269'>http://tools.ietf.org/html/rfc3269</link>&gt;.</note>" >
 <!ENTITY rfc3261 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3261'>RFC 3261</link></span> <note>RFC 3261: Session Initiation Protocol &lt;<link url='http://tools.ietf.org/html/rfc3261'>http://tools.ietf.org/html/rfc3261</link>&gt;.</note>" >
+<!ENTITY rfc3281 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3281'>RFC 3281</link></span> <note>RFC 3281: An Internet Attribute Certificate Profile for Authorization &lt;<link url='http://tools.ietf.org/html/rfc3281'>http://tools.ietf.org/html/rfc3281</link>&gt;.</note>" >
 <!ENTITY rfc3288 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3288'>RFC 3288</link></span> <note>RFC 3288: Using the Simple Object Access Protocol (SOAP) in Blocks Extensible Exchange Protocol (BEEP) &lt;<link url='http://tools.ietf.org/html/rfc3288'>http://tools.ietf.org/html/rfc3288</link>&gt;.</note>" >
 <!ENTITY rfc3312 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3312'>RFC 3312</link></span> <note>RFC 3312: Integration of Resource Management and Session Initiation Protocol (SIP) &lt;<link url='http://tools.ietf.org/html/rfc3312'>http://tools.ietf.org/html/rfc3312</link>&gt;.</note>" >
 <!ENTITY rfc3330 "<span class='ref'><link url='http://tools.ietf.org/html/rfc3330'>RFC 3330</link></span> <note>RFC 3330: Special-Use IPv4 Addresses &lt;<link url='http://tools.ietf.org/html/rfc3330'>http://tools.ietf.org/html/rfc3330</link>&gt;.</note>" >