diff --git a/CHANGELOG.md b/CHANGELOG.md
index 542a5d8..a46c562 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 # Popover Attribute Polyfill Changelog
 
-## Unreleased
+## 0.4.0: 2024-02-08
 
 - 🚀 NEW: Add support for CSS cascade layers --
   [#178](https://github.com/oddbird/popover-polyfill/pull/178)
diff --git a/package-lock.json b/package-lock.json
index bccbadb..fc3c34a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@oddbird/popover-polyfill",
-  "version": "0.3.8",
+  "version": "0.4.0",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "@oddbird/popover-polyfill",
-      "version": "0.3.8",
+      "version": "0.4.0",
       "license": "BSD-3-Clause",
       "devDependencies": {
         "@playwright/test": "1.33.0",
diff --git a/package.json b/package.json
index 07216b7..d5f7ef1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@oddbird/popover-polyfill",
-  "version": "0.3.8",
+  "version": "0.4.0",
   "description": "Popover Attribute Polyfill",
   "license": "BSD-3-Clause",
   "publishConfig": {