Improve performance of FormatDecisionState object copying
diff --git a/CHANGELOG b/CHANGELOG
index ca340a8..71246f1 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -3,6 +3,9 @@
 # This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [0.16.1] UNRELEASED
+### Changed
+- Improved performance of cloning the format decision state object. This
+  improved the time in one *large* case from 273.485s to 234.652s.
 ### Fixed
 - Ensure splitting of arguments if there's a named assign present.
 - Prefer to coalesce opening brackets if it's not at the beginning of a