diff --git a/doc/maintainers.rdoc b/doc/maintainers.rdoc
index 06146d4d45..e5f5b1865e 100644
--- a/doc/maintainers.rdoc
+++ b/doc/maintainers.rdoc
@@ -80,8 +80,6 @@ Zachary Scott (zzak)
   _unmaintained_
 [lib/open-uri.rb]
   Tanaka Akira (akr)
-[lib/open3.rb]
-  _unmaintained_
 [lib/optparse.rb, lib/optparse/*]
   Nobuyuki Nakada (nobu)
 [lib/pp.rb]
@@ -207,6 +205,10 @@ Zachary Scott (zzak)
   Keiju ISHITSUKA (keiju)
   https://github.com/ruby/mutex_m
   https://rubygems.org/gems/mutex_m
+[lib/open3.rb]
+  _unmaintained_
+  https://github.com/ruby/open3
+  https://rubygems.org/gems/open3
 [lib/ostruct.rb]
   Marc-Andre Lafortune (marcandre)
   https://github.com/ruby/ostruct
diff --git a/doc/standard_library.rdoc b/doc/standard_library.rdoc
index 7517c3e288..ca12529846 100644
--- a/doc/standard_library.rdoc
+++ b/doc/standard_library.rdoc
@@ -28,7 +28,6 @@ Net::POP3:: Ruby client library for POP3
 Net::SMTP:: Simple Mail Transfer Protocol client library for Ruby
 Observable:: Provides a mechanism for publish/subscribe pattern in Ruby
 OpenURI:: An easy-to-use wrapper for Net::HTTP, Net::HTTPS and Net::FTP
-Open3:: Provides access to stdin, stdout and stderr when running other programs
 OptionParser:: Ruby-oriented class for command-line option analysis
 PP:: Provides a PrettyPrinter for Ruby objects
 PrettyPrinter:: Implements a pretty printing algorithm for readable structure
@@ -80,6 +79,7 @@ IRB:: Interactive Ruby command-line tool for REPL (Read Eval Print Loop)
 Logger:: Provides a simple logging utility for outputting messages
 Matrix:: Represents a mathematical matrix.
 Mutex_m:: Mixin to extend objects to be handled like a Mutex
+Open3:: Provides access to stdin, stdout and stderr when running other programs
 OpenStruct:: Class to build custom data structures, similar to a Hash
 Prime:: Prime numbers and factorization library
 Racc:: A LALR(1) parser generator written in Ruby.
diff --git a/lib/open3/open3.gemspec b/lib/open3/open3.gemspec
new file mode 100644
index 0000000000..65ddaa4723
--- /dev/null
+++ b/lib/open3/open3.gemspec
@@ -0,0 +1,29 @@
+begin
+  require_relative "lib/open3/version"
+rescue LoadError # Fallback to load version file in ruby core repository
+  require_relative "version"
+end
+
+Gem::Specification.new do |spec|
+  spec.name          = "open3"
+  spec.version       = Open3::VERSION
+  spec.authors       = ["Yukihiro Matsumoto"]
+  spec.email         = ["matz@ruby-lang.org"]
+
+  spec.summary       = %q{Popen, but with stderr, too}
+  spec.description   = spec.summary
+  spec.homepage      = "https://github.com/ruby/open3"
+  spec.license       = "BSD-2-Clause"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = spec.homepage
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
+    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  end
+  spec.bindir        = "exe"
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+end
diff --git a/lib/open3/version.rb b/lib/open3/version.rb
new file mode 100644
index 0000000000..c670b79ebc
--- /dev/null
+++ b/lib/open3/version.rb
@@ -0,0 +1,3 @@
+module Open3
+  VERSION = "0.1.0"
+end
diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index 594f6d2984..fef9751cd9 100644
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -34,6 +34,7 @@
 # * https://github.com/ruby/mutex_m
 # * https://github.com/ruby/racc
 # * https://github.com/ruby/singleton
+# * https://github.com/ruby/open3
 #
 
 require 'fileutils'
@@ -74,7 +75,8 @@ $repositories = {
   e2mmap: "ruby/e2mmap",
   mutex_m: "ruby/mutex_m",
   racc: "ruby/racc",
-  singleton: "ruby/singleton"
+  singleton: "ruby/singleton",
+  open3: "ruby/open3",
 }
 
 def sync_default_gems(gem)