diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2f59a042..4b5570e0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,8 @@ Note: In this file, do not use the hard wrap in the middle of a sentence for com
 
 ## [Unreleased]
 
+- Support `mdbook`. ([#2](https://github.com/taiki-e/install-action/pull/4), thanks @thomcc)
+
 ## [1.2.2] - 2022-03-18
 
 - Support specifying the version of `nextest`. ([#2](https://github.com/taiki-e/install-action/pull/3), thanks @sunshowers)