diff --git a/release/ReleaseNotes.adoc b/release/ReleaseNotes.adoc
index 7c8bd429..7248631e 100644
--- a/release/ReleaseNotes.adoc
+++ b/release/ReleaseNotes.adoc
@@ -28,6 +28,12 @@ Compiler
   inference doesn't otherwise determine the method to conflict with
   itself (GitHub issue #641)
 
+* Change the derived `Generic` instance for enums and tagged unions
+  to use a balanced binary tree
+  ** This significantly improves the speed and memory use of the
+     compiler on designs with large enums
+     (GitHub issue #334, discussion #414)
+
 * Use UTF-8 instead of ISO-8859-1 for all text-like I/O (GitHub PR #601)
   ** Source files can now include non-Latin characters!