diff --git a/UPGRADE.txt b/UPGRADE.txt
index c009b0004b241600b2a31bd54adf6b77dd4e3ff3..e0a6f21b7414a64de0013225dd86e8dca4584c40 100644
--- a/UPGRADE.txt
+++ b/UPGRADE.txt
@@ -223,6 +223,15 @@ chan_sip:
  - Setting of HASH(SIP_CAUSE,<slave-channel-name>) on channels is now disabled
    by default. It can be enabled using the 'storesipcause' option. This feature
    has a significant performance penalty.
+ - In order to improve compliance with RFC 3261, SIP usernames are now properly
+   escaped when encoding reserved characters. Prior to this change, the use of
+   these characters in certain SIP settings affecting usernames could cause
+   injections of these characters in their raw form into SIP headers which could
+   in turn cause all sorts of nasty behaviors. All characters that are not
+   alphanumeric or are not contained in the the following lists specified by
+   RFC 3261 section 25.1 will be escaped as %XX when encoding a SIP username:
+    * mark: "-" / "_" / "." / "!" / "~" / "*" / "'" / "(" / ")"
+    * user-unreserved: "&" / "=" / "+" / "$" / "," / ";" / "?" / "/"
 
 UDPTL:
  - The default UDPTL port range in udptl.conf.sample differed from the defaults