diff --git a/RELEASE-NOTES-1.21 b/RELEASE-NOTES-1.21
index 70c6bf86b9a..7c932eff117 100644
--- a/RELEASE-NOTES-1.21
+++ b/RELEASE-NOTES-1.21
@@ -40,6 +40,7 @@ production.
 * The <data>, <time>, <meta>, and <link> elements are allowed within WikiText
   for use with Microdata.
 * The HTML5 <mark> tag has been whitelisted.
+* Added ParserCloned hook for when the Parser object is cloned.
 
 === Bug fixes in 1.21 ===
 * (bug 40353) SpecialDoubleRedirect should support interwiki redirects.