diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index d6f260a..956e895 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -31,6 +31,7 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
+          - '4.0'
           - 3.4
           - 3.3
           - 3.2
diff --git a/Gemfile.lock b/Gemfile.lock
index 3b2ebb4..3f8fbc1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -74,7 +74,6 @@ PLATFORMS
 DEPENDENCIES
   appraisal (~> 2.2.0)
   base64 (~> 0.2)
-  bundler (>= 1.17, < 3)
   byebug (~> 11.0)
   cose!
   rake (~> 13.0)
diff --git a/cose.gemspec b/cose.gemspec
index 4a217ff..96059ac 100644
--- a/cose.gemspec
+++ b/cose.gemspec
@@ -36,7 +36,6 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency "appraisal", "~> 2.2.0"
   spec.add_development_dependency "base64", "~> 0.2"
-  spec.add_development_dependency "bundler", ">= 1.17", "< 3"
   spec.add_development_dependency "byebug", "~> 11.0"
   spec.add_development_dependency "rake", "~> 13.0"
   spec.add_development_dependency "rspec", "~> 3.8"