diff --git a/doc/maintainers.rdoc b/doc/maintainers.rdoc
index 4b8a02907b..00632c73c2 100644
--- a/doc/maintainers.rdoc
+++ b/doc/maintainers.rdoc
@@ -38,8 +38,6 @@ Zachary Scott (zzak)
 
 === Libraries
 
-[lib/base64.rb]
-  Yusuke Endoh (mame)
 [lib/drb.rb, lib/drb/*]
   Masatoshi SEKI (seki)
 [lib/debug.rb]
@@ -105,6 +103,9 @@ Zachary Scott (zzak)
 [lib/abbrev.rb]
   Akinori MUSHA (knu)
   https://github.com/ruby/abbrev
+[lib/base64.rb]
+  https://github.com/ruby/base64
+  Yusuke Endoh (mame)
 [lib/benchmark.rb]
   _unmaintained_
   https://github.com/ruby/benchmark
diff --git a/doc/standard_library.rdoc b/doc/standard_library.rdoc
index 74d9301b09..c226ca48d9 100644
--- a/doc/standard_library.rdoc
+++ b/doc/standard_library.rdoc
@@ -8,7 +8,6 @@ description.
 
 == Libraries
 
-Base64:: Support for encoding and decoding binary data using a Base64 representation
 DEBUGGER__:: Debugging functionality for Ruby
 DRb:: Distributed object system for Ruby
 MakeMakefile:: Module used to generate a Makefile for C extensions
@@ -41,6 +40,7 @@ WIN32OLE:: Provides an interface for OLE Automation in Ruby
 == Libraries
 
 Abbrev:: Calculates a set of unique abbreviations for a given set of strings
+Base64:: Support for encoding and decoding binary data using a Base64 representation
 Benchmark:: Provides methods to measure and report the time used to execute code
 Bundler:: Manage your Ruby application's gem dependencies
 CGI:: Support for the Common Gateway Interface protocol
diff --git a/lib/base64.gemspec b/lib/base64.gemspec
new file mode 100644
index 0000000000..331ecc4491
--- /dev/null
+++ b/lib/base64.gemspec
@@ -0,0 +1,22 @@
+Gem::Specification.new do |spec|
+  spec.name          = "base64"
+  spec.version       = "0.1.0"
+  spec.authors       = ["Yusuke Endoh"]
+  spec.email         = ["mame@ruby-lang.org"]
+
+  spec.summary       = %q{Support for encoding and decoding binary data using a Base64 representation.}
+  spec.description   = %q{Support for encoding and decoding binary data using a Base64 representation.}
+  spec.homepage      = "https://github.com/ruby/base64"
+  spec.required_ruby_version = Gem::Requirement.new(">= 2.3.0")
+  spec.licenses      = ["Ruby", "BSD-2-Clause"]
+
+  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)/}) }
+  end
+  spec.bindir        = "exe"
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+end
diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index a787c87d0f..517f048b35 100644
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -70,6 +70,7 @@ REPOSITORIES = {
   tsort: "ruby/tsort",
   abbrev: "ruby/abbrev",
   shellwords: "ruby/shellwords",
+  base64: "ruby/base64",
 }
 
 def sync_default_gems(gem)