diff --git a/Rakefile b/Rakefile
index 9c28f2e..296bdaf 100644
--- a/Rakefile
+++ b/Rakefile
@@ -3,63 +3,17 @@ require "rake/testtask"
 
 name = "stringio"
 
+require 'rake/extensiontask'
+extask = Rake::ExtensionTask.new(name) do |x|
+  x.lib_dir << "/#{RUBY_VERSION}/#{x.platform}"
+end
 Rake::TestTask.new(:test) do |t|
-  ENV["RUBYOPT"] = "-Ilib"
-  t.libs << "test" << "test/lib"
+  ENV["RUBYOPT"] = "-I" + [extask.lib_dir, "test/lib"].join(File::PATH_SEPARATOR)
+  t.libs << extask.lib_dir
+  t.libs << "test/lib"
   t.ruby_opts << "-rhelper"
   t.test_files = FileList["test/**/test_*.rb"]
 end
 
-task :sync_tool do
-  require 'fileutils'
-  FileUtils.cp "../ruby/tool/lib/core_assertions.rb", "./test/lib"
-  FileUtils.cp "../ruby/tool/lib/envutil.rb", "./test/lib"
-  FileUtils.cp "../ruby/tool/lib/find_executable.rb", "./test/lib"
-end
-
-require 'rake/extensiontask'
-Rake::ExtensionTask.new(name)
-
-task :default => [:compile, :test]
-
-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
-
-helper = Bundler::GemHelper.instance
-def helper.version=(v)
-  gemspec.version = v
-  tag_version
-end
-
-def helper.tag_version
-  v = version.to_s
-  src = "ext/stringio/stringio.c"
-  File.open(File.join(__dir__, src), "r+b") do |f|
-    code = f.read
-    code.sub!(/^#define\s+STRINGIO_VERSION\s+\K".*"/) {v.dump}
-    f.rewind
-    f.write(code)
-    f.truncate(f.pos)
-  end
-  # system("git", "--no-pager", "-C", __dir__, "diff", "-U0", src, exception: true)
-  system("git", "-C", __dir__, "commit", "-mBump version to #{version}", src, exception: true)
-  super
-end
-
-major, minor, teeny = helper.gemspec.version.segments
-
-task "bump:teeny" do
-  helper.version = Gem::Version.new("#{major}.#{minor}.#{teeny+1}")
-end
-
-task "bump:minor" do
-  helper.version = Gem::Version.new("#{major}.#{minor+1}.0")
-end
-
-task "bump:major" do
-  helper.version = Gem::Version.new("#{major+1}.0.0")
-end
-
-task "bump" => "bump:teeny"
+task :default => :test
+task :test => :compile