diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index df65a50e9..cf11c9be5 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -11,7 +11,7 @@ jobs:
       with:
         ruby-version: '3.0'
     - name: Install dependencies
-      run: gem install minitest
+      run: gem install minitest -v "5.15.0"
     - name: Run test
       env:
         COVERALLS: "yes"
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 9fdeae227..48df02b7c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -22,6 +22,6 @@ jobs:
       with:
         ruby-version: ${{ matrix.ruby }}
     - name: Install dependencies
-      run: gem install minitest
+      run: gem install minitest -v "5.15.0"
     - name: Run test
       run: ruby -Ilib exe/rake
diff --git a/Gemfile b/Gemfile
index 8861d8470..777cab330 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,7 +4,7 @@ gemspec
 
 group :development do
   gem "bundler"
-  gem "minitest"
+  gem "minitest", "5.15.0"
   gem "coveralls"
   gem "rubocop", "~> 1.12.1"
 end