diff --git a/.github/workflows/test-jruby.yml b/.github/workflows/test-jruby.yml
new file mode 100644
index 0000000..e56eab8
--- /dev/null
+++ b/.github/workflows/test-jruby.yml
@@ -0,0 +1,21 @@
+name: test
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: build (${{ matrix.ruby }} / ${{ matrix.os }})
+    strategy:
+      matrix:
+        ruby: [ 2.7, 2.6, head, jruby-9.3 ]
+        os: [ ubuntu-latest, macos-latest ]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true # 'bundle install' and cache
+    - name: Run test
+      run: bundle exec rake test
diff --git a/lib/open3.rb b/lib/open3.rb
index c574696..9652b27 100644
--- a/lib/open3.rb
+++ b/lib/open3.rb
@@ -29,8 +29,9 @@
 # - Open3.pipeline : run a pipeline and wait for its completion
 #
 
+require 'open3/version'
+
 module Open3
-  VERSION = "0.1.1"
 
   # Open stdin, stdout, and stderr streams and start external executable.
   # In addition, a thread to wait for the started process is created.
@@ -758,3 +759,6 @@ class << self
   end
 
 end
+
+# JRuby uses different popen logic on Windows, require it here to reuse wrapper methods above.
+require 'open3/jruby_windows' if RUBY_ENGINE == 'jruby' && JRuby::Util::ON_WINDOWS
diff --git a/lib/open3/jruby_windows.rb b/lib/open3/jruby_windows.rb
new file mode 100644
index 0000000..064c38b
--- /dev/null
+++ b/lib/open3/jruby_windows.rb
@@ -0,0 +1,127 @@
+#
+# Custom implementation of Open3.popen{3,2,2e} that uses java.lang.ProcessBuilder rather than pipes and spawns.
+#
+
+require 'jruby' # need access to runtime for RubyStatus construction
+
+module Open3
+
+  java_import java.lang.ProcessBuilder
+  java_import org.jruby.RubyProcess
+  java_import org.jruby.util.ShellLauncher
+
+  def popen3(*cmd, &block)
+    if cmd.size > 0 && Hash === cmd[-1]
+      opts = cmd.pop
+    else
+      opts = {}
+    end
+    processbuilder_run(cmd, opts, io: IO_3, &block)
+  end
+  module_function :popen3
+
+  IO_3 = proc do |process|
+    [process.getOutputStream.to_io, process.getInputStream.to_io, process.getErrorStream.to_io]
+  end
+
+  BUILD_2 = proc do |builder|
+    builder.redirectError(ProcessBuilder::Redirect::INHERIT)
+  end
+
+  IO_2 = proc do |process|
+    [process.getOutputStream.to_io, process.getInputStream.to_io]
+  end
+
+  def popen2(*cmd, &block)
+    if cmd.size > 0 && Hash === cmd[-1]
+      opts = cmd.pop
+    else
+      opts = {}
+    end
+    processbuilder_run(cmd, opts, build: BUILD_2, io: IO_2, &block)
+  end
+  module_function :popen2
+
+  BUILD_2E = proc do |builder|
+    builder.redirectErrorStream(true)
+  end
+
+  def popen2e(*cmd, &block)
+    if cmd.size > 0 && Hash === cmd[-1]
+      opts = cmd.pop
+    else
+      opts = {}
+    end
+    processbuilder_run(cmd, opts, build: BUILD_2E, io: IO_2, &block)
+  end
+  module_function :popen2e
+
+  def processbuilder_run(cmd, opts, build: nil, io:)
+    opts.each do |k, v|
+      if Integer === k
+        if IO == v || !(String === v || v.respond_to?(:to_path))
+          # target is an open IO or a non-pathable object, bail out
+          raise NotImplementedError.new("redirect to an open IO is not implemented on this platform")
+        end
+      end
+    end
+
+    if Hash === cmd[0]
+      env = cmd.shift;
+    else
+      env = {}
+    end
+
+    if cmd.size == 1 && (cmd[0] =~ / / || ShellLauncher.shouldUseShell(cmd[0]))
+      cmd = [RbConfig::CONFIG['SHELL'], JRuby::Util::ON_WINDOWS ? '/c' : '-c', cmd[0]]
+    end
+
+    builder = ProcessBuilder.new(cmd.to_java(:string))
+
+    builder.directory(java.io.File.new(opts[:chdir] || Dir.pwd))
+
+    environment = builder.environment
+    env.each { |k, v| v.nil? ? environment.remove(k) : environment.put(k, v) }
+
+    build.call(builder) if build
+
+    process = builder.start
+
+    pid = org.jruby.util.ShellLauncher.getPidFromProcess(process)
+
+    parent_io = io.call(process)
+
+    parent_io.each {|i| i.sync = true}
+
+    wait_thr = DetachThread.new(pid) { RubyProcess::RubyStatus.newProcessStatus(JRuby.runtime, process.waitFor << 8, pid) }
+
+    result = [*parent_io, wait_thr]
+
+    if defined? yield
+      begin
+        return yield(*result)
+      ensure
+        parent_io.each(&:close)
+        wait_thr.join
+      end
+    end
+
+    result
+  end
+  module_function :processbuilder_run
+  class << self
+    private :processbuilder_run
+  end
+
+  class DetachThread < Thread
+    attr_reader :pid
+
+    def initialize(pid)
+      super
+
+      @pid = pid
+      self[:pid] = pid
+    end
+  end
+
+end
diff --git a/lib/open3/version.rb b/lib/open3/version.rb
new file mode 100644
index 0000000..5a8e84b
--- /dev/null
+++ b/lib/open3/version.rb
@@ -0,0 +1,3 @@
+module Open3
+  VERSION = "0.1.1"
+end
diff --git a/open3.gemspec b/open3.gemspec
index ad9485a..89c2cbe 100644
--- a/open3.gemspec
+++ b/open3.gemspec
@@ -1,10 +1,8 @@
 # frozen_string_literal: true
 
 name = File.basename(__FILE__, ".gemspec")
-version = ["lib", Array.new(name.count("-"), "..").join("/")].find do |dir|
-  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb")) do |line|
-    /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
-  end rescue nil
+version = File.foreach(File.join(__dir__, "lib/open3/version.rb")) do |line|
+  /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
 end
 
 Gem::Specification.new do |spec|
diff --git a/test/test_open3.rb b/test/test_open3.rb
index 47d471c..36ccd4c 100644
--- a/test/test_open3.rb
+++ b/test/test_open3.rb
@@ -2,7 +2,10 @@
 
 require 'test/unit'
 require 'open3'
-require_relative 'lib/jit_support'
+
+if RUBY_ENGINE == 'ruby'
+  require_relative 'lib/jit_support'
+end
 
 class TestOpen3 < Test::Unit::TestCase
   RUBY = EnvUtil.rubybin
@@ -92,7 +95,7 @@ def test_numeric_file_descriptor2
   end
 
   def test_numeric_file_descriptor3
-    skip "passing FDs bigger than 2 is not supported on Windows" if /mswin|mingw/ =~ RUBY_PLATFORM
+    skip "passing FDs bigger than 2 is not supported on Windows" if /mswin|mingw/ =~ RbConfig::CONFIG['host_os']
     with_pipe {|r, w|
       Open3.popen3(RUBY, '-e', 'IO.open(3).puts "foo"', 3 => w) {|i,o,e,t|
         assert_equal("foo\n", r.gets, "[GH-808] [ruby-core:67347] [Bug #10699]")
@@ -127,7 +130,11 @@ def test_popen2
           i.close
           STDERR.reopen(old)
           assert_equal("zo", o.read)
-          assert_equal("ze", JITSupport.remove_mjit_logs(r.read))
+          if defined?(JITSupport)
+            assert_equal("ze", JITSupport.remove_mjit_logs(r.read))
+          else
+            assert_equal("ze", r.read)
+          end
         }
       }
     }