diff --git a/xep.ent b/xep.ent
index 34aa9ba6..940e702d 100644
--- a/xep.ent
+++ b/xep.ent
@@ -544,6 +544,7 @@ THE SOFTWARE.
 <!ENTITY rfc4480 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4480'>RFC 4480</link></span> <note>RFC 4480: RPID: Rich Presence Extensions to the Presence Information Data Format (PIDF) &lt;<link url='http://tools.ietf.org/html/rfc4480'>http://tools.ietf.org/html/rfc4480</link>&gt;.</note>" >
 <!ENTITY rfc4481 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4481'>RFC 4481</link></span> <note>RFC 4481: Timed Presence Extensions to the Presence Information Data Format (PIDF) to Indicate Status Information for Past and Future Time Intervals &lt;<link url='http://tools.ietf.org/html/rfc4481'>http://tools.ietf.org/html/rfc4481</link>&gt;.</note>" >
 <!ENTITY rfc4505 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4505'>RFC 4505</link></span> <note>RFC 4505: The SASL ANONYMOUS Mechanism &lt;<link url='http://tools.ietf.org/html/rfc4505'>http://tools.ietf.org/html/rfc4505</link>&gt;.</note>" >
+<!ENTITY rfc4551 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4551'>RFC 4551</link></span> <note>RFC 4551: IMAP Extension for Conditional STORE Operation or Quick Flag Changes Resynchronization &lt;<link url='http://tools.ietf.org/html/rfc4551'>http://tools.ietf.org/html/rfc4551</link>&gt;.</note>" >
 <!ENTITY rfc4566 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4566'>RFC 4566</link></span> <note>RFC 4566: SDP: Session Description Protocol &lt;<link url='http://tools.ietf.org/html/rfc4566'>http://tools.ietf.org/html/rfc4566</link>&gt;.</note>" >
 <!ENTITY rfc4568 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4568'>RFC 4568</link></span> <note>RFC 4568: Session Description Protocol (SDP) Security Descriptions for Media Streams &lt;<link url='http://tools.ietf.org/html/rfc4568'>http://tools.ietf.org/html/rfc4568</link>&gt;.</note>" >
 <!ENTITY rfc4571 "<span class='ref'><link url='http://tools.ietf.org/html/rfc4571'>RFC 4571</link></span> <note>RFC 4571: Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport &lt;<link url='http://tools.ietf.org/html/rfc4571'>http://tools.ietf.org/html/rfc4571</link>&gt;.</note>" >