diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index e89e24d..7781208 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -66,6 +66,16 @@ jobs:
         - ruby: 3.4.1
           gemfile: Gemfile.8.0.pg
           bundler: 2.5.23
+
+        - ruby: 4.0.2
+          gemfile: Gemfile.6.1.pg
+          bundler: 2.5.23
+        - ruby: 4.0.2
+          gemfile: Gemfile.7.0.pg
+          bundler: 2.5.23
+        - ruby: 4.0.2
+          gemfile: Gemfile.8.0.pg
+          bundler: 2.5.23
     env:
       BUNDLE_GEMFILE: "${{ matrix.gemfile }}"
     steps:
diff --git a/.ruby-version b/.ruby-version
index 47b322c..4d54dad 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.1
+4.0.2
diff --git a/README.md b/README.md
index 69dbdda..4385ab8 100644
--- a/README.md
+++ b/README.md
@@ -191,7 +191,7 @@ We recommend to test large changes against multiple versions of Ruby and multipl
 - Run tests using `rake matrix:spec`
 
   ```sh
-  for version in "2.5.6" "2.6.6" "2.7.2" "3.2.0" "3.4.1"; do rbenv shell $version && bundle install && bundle exec rake matrix:install && bundle exec rake matrix:spec; done
+  for version in "2.5.6" "2.6.6" "2.7.2" "3.2.0" "3.4.1" "4.0.2"; do rbenv shell $version && bundle install && bundle exec rake matrix:install && bundle exec rake matrix:spec; done
   ```
 
 You can also run `bin/console` for an interactive prompt that will allow you to experiment.