diff --git a/source/whats-new.txt b/source/whats-new.txt
index 9769d357..116535d2 100644
--- a/source/whats-new.txt
+++ b/source/whats-new.txt
@@ -172,6 +172,13 @@ This release includes the following improvements and fixes:
 
 - The ``Collection.Clone()`` method does not return an error.
 
+- Renames the ``canonical`` parameter of the ``UnmarshalExtJSON()``
+  method to ``canonicalOnly``. If you set ``canonicalOnly`` to ``true``,
+  the method returns an error if the extended JSON is not marshaled in
+  canonical mode. If set to ``false``, the method can unmarshal
+  canonical or relaxed extended JSON. To learn more, see the
+  `UnmarshalExtJSON() <{+api+}/bson#UnmarshalExtJSON>`__ API documentation.
+
 .. _golang-version-1.17:
 
 What's New in 1.17