diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 21bb462..6003335 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -23,14 +23,15 @@ jobs:
           - 3.2
           - 3.3
           - 3.4
+          - 4.0
         mongo-image:
           - mongo:4.4
         include:
-          - { "ruby-version": 3.3, "mongo-image": "mongo:4.2" }
-          - { "ruby-version": 3.3, "mongo-image": "mongo:5.0" }
-          - { "ruby-version": 3.3, "mongo-image": "mongo:6.0" }
-          - { "ruby-version": 3.3, "mongo-image": "mongo:7.0" }
-          - { "ruby-version": 3.3, "mongo-image": "mongo:8.0" }
+          - { "ruby-version": 4.0, "mongo-image": "mongo:4.2" }
+          - { "ruby-version": 4.0, "mongo-image": "mongo:5.0" }
+          - { "ruby-version": 4.0, "mongo-image": "mongo:6.0" }
+          - { "ruby-version": 4.0, "mongo-image": "mongo:7.0" }
+          - { "ruby-version": 4.0, "mongo-image": "mongo:8.0" }
     services:
       mongo:
         image: ${{ matrix.mongo-image }}
@@ -43,7 +44,10 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: "${{ matrix.ruby-version }}"
+        bundler-cache: false
+    - name: Set up bundler
+      run: bundle config set --local without "guard"
     - name: Install dependencies
-      run: "bundle install --without guard"
+      run: "bundle install"
     - name: Run tests
       run: "bundle exec rake"
diff --git a/Gemfile b/Gemfile
index ec8020e..0194885 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,6 +8,11 @@ if RUBY_VERSION >= '3.4'
   gem 'bigdecimal'
 end
 
+if RUBY_VERSION >= '4.0'
+  # the mongo gem depends on the logger gem, which has been extracted as a bundled gem since Ruby 4.0.
+  gem 'logger'
+end
+
 group(:test) do
   gem 'rspec'
   gem 'log_buddy'