diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b1d09e6..c22cf64 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['3.3', '3.4', 'jruby']
+        ruby-version: ['3.3', '3.4', '4.0', 'jruby']
 
     steps:
       - uses: actions/checkout@v4
diff --git a/.rubocop.yml b/.rubocop.yml
index 7d06dab..fe2ba76 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,4 +1,4 @@
-require:
+plugins:
   - rubocop-performance
   - rubocop-rake
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 5998768..3895830 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -82,4 +82,4 @@ DEPENDENCIES
   webrick
 
 BUNDLED WITH
-   2.4.12
+  4.0.3