diff --git a/CHANGELOG.md b/CHANGELOG.md
index 747a1f5..5055402 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic versioning](http://semver.org/).
 
+## [3.1.1]
+
+- add type hints to `OppositeSemigroup` and `OppositeMonoid`
+
 ## [3.1.0]
 
 - add `voidRight` in `ExtraFunctor`