diff --git a/.gitignore b/.gitignore
index b621a3e9..8ae6ac11 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,3 +20,5 @@ Gemfile.lock
 */**/*.jar
 .byebug_history
 *.log
+/tmp
+
diff --git a/Gemfile b/Gemfile
index 3d74f7ff..50249b0c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,27 +1,23 @@
-# vim: set ft=ruby:
-
 source 'https://rubygems.org'
 
-case ENV['JSON']
-when 'ext', nil
-  if ENV['RUBY_ENGINE'] == 'jruby'
-    gemspec :name => 'json-java'
-  else
-    gemspec :name => 'json'
-  end
-when 'pure'
-  gemspec :name => 'json_pure'
+if ENV['JSON'] == 'pure'
+  gemspec name: 'json_pure'
+else
+  gemspec name: 'json'
 end
 
-gem "rake"
-gem "test-unit"
-gem "test-unit-ruby-core"
-gem "all_images", "~> 0" unless RUBY_PLATFORM =~ /java/
+group :development do
+  gem "rake"
+  gem "rake-compiler"
+  gem "test-unit"
+  gem "test-unit-ruby-core"
+  gem "all_images", "~> 0" unless RUBY_PLATFORM =~ /java/
 
-if ENV['BENCHMARK']
-  gem "benchmark-ips"
-  unless RUBY_PLATFORM =~ /java/
-    gem "oj"
-    gem "rapidjson"
+  if ENV['BENCHMARK']
+    gem "benchmark-ips"
+    unless RUBY_PLATFORM =~ /java/
+      gem "oj"
+      gem "rapidjson"
+    end
   end
 end
diff --git a/README.md b/README.md
index 3b0b6ebf..94a35d7b 100644
--- a/README.md
+++ b/README.md
@@ -231,7 +231,7 @@ the `pp` library's `pp` methods.
 
 ### Release
 
-Update the json.gemspec and json-java.gemspec.
+Update the `lib/json/version.rb` file.
 
 ```
 rbenv shell 2.6.5
diff --git a/Rakefile b/Rakefile
index 81e8bd9b..307b86d3 100644
--- a/Rakefile
+++ b/Rakefile
@@ -191,9 +191,8 @@ if defined?(RUBY_ENGINE) and RUBY_ENGINE == 'jruby'
 
   desc "Package the jruby gem"
   task :jruby_gem => :create_jar do
-    sh 'gem build json-java.gemspec'
     mkdir_p 'pkg'
-    mv "json-#{PKG_VERSION}-java.gem", 'pkg'
+    sh "gem build -o pkg/json-#{PKG_VERSION}-java.gem json.gemspec"
   end
 
   desc "Testing library (jruby)"
diff --git a/ext/json/extconf.rb b/ext/json/extconf.rb
deleted file mode 100644
index 8a99b6a5..00000000
--- a/ext/json/extconf.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-require 'mkmf'
-
-create_makefile('json')
diff --git a/json-java.gemspec b/json-java.gemspec
deleted file mode 100644
index ad357c88..00000000
--- a/json-java.gemspec
+++ /dev/null
@@ -1,36 +0,0 @@
-version = File.foreach(File.join(__dir__, "lib/json/version.rb")) do |line|
-  /^\s*VERSION\s*=\s*'(.*)'/ =~ line and break $1
-end rescue nil
-
-spec = Gem::Specification.new do |s|
-  s.name = "json"
-  s.version = version
-
-  s.summary = "JSON Implementation for Ruby"
-  s.description = "A JSON implementation as a JRuby extension."
-  s.licenses = ["Ruby"]
-  s.author = "Daniel Luz"
-  s.email = "dev+ruby@mernen.com"
-
-  s.platform = 'java'
-
-  s.files = Dir["lib/**/*", "COPYING", "LEGAL", "BSDL"]
-
-  s.homepage = "https://ruby.github.io/json"
-  s.metadata = {
-      'bug_tracker_uri'   => 'https://github.com/ruby/json/issues',
-      'changelog_uri'     => 'https://github.com/ruby/json/blob/master/CHANGES.md',
-      'documentation_uri' => 'https://ruby.github.io/json/doc/index.html',
-      'homepage_uri'      => s.homepage,
-      'source_code_uri'   => 'https://github.com/ruby/json',
-      'wiki_uri'          => 'https://github.com/ruby/json/wiki'
-  }
-
-  s.required_ruby_version = Gem::Requirement.new(">= 2.3")
-end
-
-if $0 == __FILE__
-  Gem::Builder.new(spec).build
-else
-  spec
-end
diff --git a/json.gemspec b/json.gemspec
index 39b0155d..96721f90 100644
--- a/json.gemspec
+++ b/json.gemspec
@@ -2,70 +2,60 @@ version = File.foreach(File.join(__dir__, "lib/json/version.rb")) do |line|
   /^\s*VERSION\s*=\s*'(.*)'/ =~ line and break $1
 end rescue nil
 
-Gem::Specification.new do |s|
+spec = Gem::Specification.new do |s|
+  java_ext = Gem::Platform === s.platform && s.platform =~ 'java' || RUBY_ENGINE == 'jruby'
+
   s.name = "json"
   s.version = version
 
   s.summary = "JSON Implementation for Ruby"
-  s.description = "This is a JSON implementation as a Ruby extension in C."
+  s.homepage = "https://ruby.github.io/json"
+  s.metadata = {
+    'bug_tracker_uri'   => 'https://github.com/ruby/json/issues',
+    'changelog_uri'     => 'https://github.com/ruby/json/blob/master/CHANGES.md',
+    'documentation_uri' => 'https://ruby.github.io/json/doc/index.html',
+    'homepage_uri'      => s.homepage,
+    'source_code_uri'   => 'https://github.com/ruby/json',
+    'wiki_uri'          => 'https://github.com/ruby/json/wiki'
+  }
+
+  s.required_ruby_version = Gem::Requirement.new(">= 2.3")
+
+  if java_ext
+    s.description = "A JSON implementation as a JRuby extension."
+    s.author = "Daniel Luz"
+    s.email = "dev+ruby@mernen.com"
+  else
+    s.description = "This is a JSON implementation as a Ruby extension in C."
+    s.authors = ["Florian Frank"]
+    s.email = "flori@ping.de"
+  end
+
   s.licenses = ["Ruby"]
-  s.authors = ["Florian Frank"]
-  s.email = "flori@ping.de"
 
-  s.extensions = ["ext/json/ext/generator/extconf.rb", "ext/json/ext/parser/extconf.rb", "ext/json/extconf.rb"]
   s.extra_rdoc_files = ["README.md"]
   s.rdoc_options = ["--title", "JSON implementation for Ruby", "--main", "README.md"]
+
   s.files = [
     "CHANGES.md",
     "COPYING",
     "BSDL",
     "LEGAL",
     "README.md",
-    "ext/json/ext/fbuffer/fbuffer.h",
-    "ext/json/ext/generator/depend",
-    "ext/json/ext/generator/extconf.rb",
-    "ext/json/ext/generator/generator.c",
-    "ext/json/ext/generator/generator.h",
-    "ext/json/ext/parser/depend",
-    "ext/json/ext/parser/extconf.rb",
-    "ext/json/ext/parser/parser.c",
-    "ext/json/ext/parser/parser.h",
-    "ext/json/ext/parser/parser.rl",
-    "ext/json/extconf.rb",
     "json.gemspec",
-    "lib/json.rb",
-    "lib/json/add/bigdecimal.rb",
-    "lib/json/add/complex.rb",
-    "lib/json/add/core.rb",
-    "lib/json/add/date.rb",
-    "lib/json/add/date_time.rb",
-    "lib/json/add/exception.rb",
-    "lib/json/add/ostruct.rb",
-    "lib/json/add/range.rb",
-    "lib/json/add/rational.rb",
-    "lib/json/add/regexp.rb",
-    "lib/json/add/set.rb",
-    "lib/json/add/struct.rb",
-    "lib/json/add/symbol.rb",
-    "lib/json/add/time.rb",
-    "lib/json/common.rb",
-    "lib/json/ext.rb",
-    "lib/json/ext/generator/state.rb",
-    "lib/json/generic_object.rb",
-    "lib/json/pure.rb",
-    "lib/json/pure/generator.rb",
-    "lib/json/pure/parser.rb",
-    "lib/json/version.rb",
+    *Dir["lib/**/*.rb"],
   ]
-  s.homepage = "https://ruby.github.io/json"
-  s.metadata = {
-    'bug_tracker_uri'   => 'https://github.com/ruby/json/issues',
-    'changelog_uri'     => 'https://github.com/ruby/json/blob/master/CHANGES.md',
-    'documentation_uri' => 'https://ruby.github.io/json/doc/index.html',
-    'homepage_uri'      => s.homepage,
-    'source_code_uri'   => 'https://github.com/ruby/json',
-    'wiki_uri'          => 'https://github.com/ruby/json/wiki'
-  }
 
-  s.required_ruby_version = Gem::Requirement.new(">= 2.3")
+  if java_ext
+    s.platform = 'java'
+  else
+    s.extensions = Dir["ext/json/**/extconf.rb"]
+    s.files += Dir["ext/json/**/*.{c,h,rl}"]
+  end
+end
+
+if RUBY_ENGINE == 'jruby' && $0 == __FILE__
+  Gem::Builder.new(spec).build
+else
+  spec
 end