diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f4e0828..59183c6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,10 +9,14 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: ['2.7', '3.0', '3.1', '3.2']
+        ruby-version:
+          - '3.2'
+          - '3.3'
+          - '3.4'
+          - 'ruby-head'
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
diff --git a/Gemfile b/Gemfile
index ea82bc2..87a1fb0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,6 +9,8 @@ group :development, :test do
   gem 'mutant',       github: 'mbj/mutant'
   gem 'mutant-rspec', github: 'mbj/mutant'
 
+  gem 'bigdecimal'
+
   source 'https://oss:sxCL1o1navkPi2XnGB5WYBrhpY9iKIPL@gem.mutant.dev' do
     gem 'mutant-license'
   end
diff --git a/config/mutant.yml b/config/mutant.yml
index 54be0c4..68d0e60 100644
--- a/config/mutant.yml
+++ b/config/mutant.yml
@@ -10,3 +10,4 @@ mutation:
   timeout: 1.0
 coverage_criteria:
   timeout: true
+usage: opensource