diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2fbf9c3..b8c8e6d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## v4.0.0
+
+- use Rust Edition 2021 (upgrade from 2018)
+
 ## v3.3.0
 
 - refactor `make_toc` function for easier third-party integration [#13](https://github.com/KevinGimbel/mktoc/issues/13)
@@ -22,4 +26,4 @@
 ## v3.0.0
 
 - Implement JSON settings
-- Add build for GitHub Binary releases
\ No newline at end of file
+- Add build for GitHub Binary releases
diff --git a/Cargo.toml b/Cargo.toml
index adda1ea..5c18981 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "mktoc"
 description = "Generate Table of Contents from Markdown files"
 license = "MIT"
-version = "3.3.0"
+version = "4.0.0"
 authors = ["Kevin Gimbel <hallo@kevingimbel.com>"]
 edition = "2021"
 repository = "https://github.com/kevingimbel/mktoc"