diff --git a/releases/2.15.md b/releases/2.15.md
index 7ddf88c..2a50d4c 100644
--- a/releases/2.15.md
+++ b/releases/2.15.md
@@ -38,6 +38,14 @@
 
 Changes can be switched between "work in progress" and "ready to review".
 
+### API
+
+* Instances of [IdString](https://gerrit.googlesource.com/gerrit/+/stable-2.15/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/restapi/IdString.java)
+  used to return true when `equals` was given a String instance equal to the
+  IdString's URL-encoded value. This violates
+  [symmetry](https://en.wikipedia.org/wiki/Equivalence_relation#Definition), so
+  this behavior was removed: IdStrings now never compare equal to Strings.
+
 ### REST API
 
 #### Changes