diff --git a/Rakefile b/Rakefile
index f32f2a8..caacbf2 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,48 +1,12 @@
 require "bundler/gem_tasks"
 require "rake/testtask"
 
-helper = Bundler::GemHelper.instance
-
 Rake::TestTask.new(:test) do |t|
   t.test_files = FileList["test/**/test_*.rb"]
 end
 
 task :default => :test
 
-task "build" => "date_epoch"
-task "build" => "changelogs"
-
-task "date_epoch" do
-  ENV["SOURCE_DATE_EPOCH"] = IO.popen(%W[git -C #{__dir__} log -1 --format=%ct], &:read).chomp
-end
-
-def helper.update_gemspec
-  path = "#{__dir__}/#{gemspec.name}.gemspec"
-  File.open(path, "r+b") do |f|
-    if (d = f.read).sub!(/^(version\s*=\s*)".*"/) {$1 + gemspec.version.to_s.dump}
-      f.rewind
-      f.truncate(0)
-      f.print(d)
-    end
-  end
-end
-
-def helper.commit_bump
-  sh(%W[git -C #{__dir__} commit -m bump\ up\ to\ #{gemspec.version}
-        #{gemspec.name}.gemspec])
-end
-
-def helper.version=(v)
-  gemspec.version = v
-  update_gemspec
-  commit_bump
-end
-major, minor, teeny = helper.gemspec.version.segments
-
-task "bump:teeny" do
-  helper.version = Gem::Version.new("#{major}.#{minor}.#{teeny+1}")
-end
-
 task "bump:minor" do
   raise "can't bump up minor"
 end
@@ -50,41 +14,3 @@ end
 task "bump:major" do
   raise "can't bump up major"
 end
-
-task "bump" => "bump:teeny"
-
-task "tag" do
-  helper.__send__(:tag_version)
-end
-
-def changelog(output, ver = nil, prev = nil)
-  ver &&= Gem::Version.new(ver)
-  range = [[prev], [ver, "HEAD"]].map {|ver, branch| ver ? "v#{ver.to_s}" : branch}.compact.join("..")
-  IO.popen(%W[git log --format=fuller --topo-order --no-merges #{range}]) do |log|
-    line = log.gets
-    FileUtils.mkpath(File.dirname(output))
-    File.open(output, "wb") do |f|
-      f.print "-*- coding: utf-8 -*-\n\n", line
-      log.each_line do |line|
-        line.sub!(/^(?!:)(?:Author|Commit)?(?:Date)?: /, '  \&')
-        line.sub!(/ +$/, '')
-        f.print(line)
-      end
-    end
-  end
-end
-
-tags = IO.popen(%w[git tag -l v0.*]).grep(/v(.*)/) {$1}
-tags.sort_by! {|tag| tag.scan(/\d+/).map(&:to_i)}
-tags.inject(nil) do |prev, tag|
-  task("logs/ChangeLog-#{tag}") {|t| changelog(t.name, tag, prev)}
-  tag
-end
-
-desc "Make ChangeLog"
-task "ChangeLog", [:ver, :prev] do |t, ver: nil, prev: tags.last|
-  changelog(t.name, ver, prev)
-end
-changelogs = ["ChangeLog", *tags.map {|tag| "logs/ChangeLog-#{tag}"}]
-task "changelogs" => changelogs
-CLOBBER.concat(changelogs) << "logs"
diff --git a/rakelib/changelogs.rake b/rakelib/changelogs.rake
new file mode 100644
index 0000000..df72f9d
--- /dev/null
+++ b/rakelib/changelogs.rake
@@ -0,0 +1,34 @@
+task "build" => "changelogs"
+
+changelog = proc do |output, ver = nil, prev = nil|
+  ver &&= Gem::Version.new(ver)
+  range = [[prev], [ver, "HEAD"]].map {|ver, branch| ver ? "v#{ver.to_s}" : branch}.compact.join("..")
+  IO.popen(%W[git log --format=fuller --topo-order --no-merges #{range}]) do |log|
+    line = log.gets
+    FileUtils.mkpath(File.dirname(output))
+    File.open(output, "wb") do |f|
+      f.print "-*- coding: utf-8 -*-\n\n", line
+      log.each_line do |line|
+        line.sub!(/^(?!:)(?:Author|Commit)?(?:Date)?: /, '  \&')
+        line.sub!(/ +$/, '')
+        f.print(line)
+      end
+    end
+  end
+end
+
+tags = IO.popen(%w[git tag -l v[0-9]*]).grep(/v(.*)/) {$1}
+tags.sort_by! {|tag| tag.scan(/\d+/).map(&:to_i)}
+tags.inject(nil) do |prev, tag|
+  task("logs/ChangeLog-#{tag}") {|t| changelog[t.name, tag, prev]}
+  tag
+end
+
+desc "Make ChangeLog"
+task "ChangeLog", [:ver, :prev] do |t, ver: nil, prev: tags.last|
+  changelog[t.name, ver, prev]
+end
+
+changelogs = ["ChangeLog", *tags.map {|tag| "logs/ChangeLog-#{tag}"}]
+task "changelogs" => changelogs
+CLOBBER.concat(changelogs) << "logs"
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/rakelib/version.rake b/rakelib/version.rake
new file mode 100644
index 0000000..c56ea56
--- /dev/null
+++ b/rakelib/version.rake
@@ -0,0 +1,44 @@
+class << (helper = Bundler::GemHelper.instance)
+  def update_gemspec
+    path = gemspec.loaded_from
+    File.open(path, "r+b") do |f|
+      d = f.read
+      if d.sub!(/^(_VERSION\s*=\s*)".*"/) {$1 + gemspec.version.to_s.dump}
+        f.rewind
+        f.truncate(0)
+        f.print(d)
+      end
+    end
+  end
+
+  def commit_bump
+    sh(%W[git -C #{__dir__} commit -m bump\ up\ to\ #{gemspec.version}
+          #{gemspec.loaded_from}])
+  end
+
+  def version=(v)
+    gemspec.version = v
+    update_gemspec
+    commit_bump
+  end
+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 "tag" do
+  helper.__send__(:tag_version)
+end
diff --git a/ruby2_keywords.gemspec b/ruby2_keywords.gemspec
index cfe7811..e2cd397 100644
--- a/ruby2_keywords.gemspec
+++ b/ruby2_keywords.gemspec
@@ -1,9 +1,9 @@
-version = "0.0.5"
-abort "Version must not reach 1" if version[/\d+/].to_i >= 1
+_VERSION = "0.0.5"
+abort "Version must not reach 1" if _VERSION[/\d+/].to_i >= 1
 
 Gem::Specification.new do |s|
   s.name = "ruby2_keywords"
-  s.version = version
+  s.version = _VERSION
   s.summary = "Shim library for Module#ruby2_keywords"
   s.homepage = "https://github.com/ruby/ruby2_keywords"
   s.licenses = ["Ruby", "BSD-2-Clause"]