diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 9a1cbdf..f62b8b7 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -26,3 +26,16 @@ jobs:
         bundler-cache: true
     - name: Run test
       run: bundle exec rake test
+    - id: build
+      run: |
+        rake build
+        echo "pkg=${GITHUB_REPOSITORY#*/}-${RUNNING_OS%-*}" >> $GITHUB_OUTPUT
+      env:
+        RUNNING_OS: ${{matrix.os}}
+      if: needs.ruby-versions.outputs.latest == matrix.ruby
+    - name: Upload package
+      uses: actions/upload-artifact@v4
+      with:
+        path: pkg/*
+        name: ${{steps.build.outputs.pkg}}
+      if: steps.build.outputs.pkg
diff --git a/Gemfile b/Gemfile
index 43ff9f2..7f1d99c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,6 +3,8 @@ source "https://rubygems.org"
 # Specify your gem's dependencies in time.gemspec
 gemspec
 
-gem "rake", "~> 12.0"
-gem "test-unit"
-gem "test-unit-ruby-core"
+group :development do
+  gem "rake", "~> 12.0"
+  gem "test-unit"
+  gem "test-unit-ruby-core"
+end
diff --git a/rakelib/epoch.rake b/rakelib/epoch.rake
new file mode 100644
index 0000000..80f27c9
--- /dev/null
+++ b/rakelib/epoch.rake
@@ -0,0 +1,5 @@
+task "build" => "date_epoch"
+
+task "date_epoch" do
+  ENV["SOURCE_DATE_EPOCH"] = IO.popen(%W[git -C #{__dir__} log -1 --format=%ct], &:read).chomp
+end
diff --git a/time.gemspec b/time.gemspec
index a9349a2..4b9f9e1 100644
--- a/time.gemspec
+++ b/time.gemspec
@@ -20,8 +20,12 @@ Gem::Specification.new do |spec|
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = spec.homepage
 
-  spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
-    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  srcdir, gemspec = File.split(__FILE__)
+  spec.files         = Dir.chdir(srcdir) do
+    `git ls-files -z`.split("\x0").reject { |f|
+      f == gemspec or
+        f.start_with?(".git", "bin/", "test/", "rakelib/", "Gemfile", "Rakefile")
+    }
   end
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }