diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 548f41a..e42e6cc 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -22,6 +22,8 @@ jobs:
           - '2.7'
           - '3.0'
           - '3.1'
+          - '3.2'
+          - '3.3'
           - 'jruby'
           - 'truffleruby'
 
@@ -30,7 +32,7 @@ jobs:
     env:
       BUNDLE_WITHOUT: 'yard pry'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
diff --git a/.ruby-version b/.ruby-version
index 94ff29c..15a2799 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.1.1
+3.3.0
diff --git a/unitwise.gemspec b/unitwise.gemspec
index 5d7c10a..8c5e747 100644
--- a/unitwise.gemspec
+++ b/unitwise.gemspec
@@ -20,6 +20,8 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(/^test\//)
   gem.require_paths = ['lib']
 
+  gem.required_ruby_version = '>= 2.6'
+
   gem.add_dependency               'liner',           '~> 0.2'
   gem.add_dependency               'signed_multiset', '~> 0.2'
   gem.add_dependency               'memoizable',      '~> 0.4'