diff --git a/circle.yml b/circle.yml
index 94d00c27..b774e4cb 100644
--- a/circle.yml
+++ b/circle.yml
@@ -1,7 +1,20 @@
 machine:
   ruby:
     version: 2.3.1
+  java:
+    version: oraclejdk8
+  environment:
+    JRUBY_OPTS: '--dev --debug'
+    JRUBY: jruby-9.1.6.0
+
+dependencies:
+  pre:
+    - echo rvm_autoupdate_flag=0 >> ~/.rvmrc
+    - rvm install $JRUBY
+  post:
+    - rvm-exec $JRUBY bundle install
 
 test:
   override:
+    - rvm-exec $JRUBY bundle exec rake test
     - bundle exec rake test
diff --git a/lib/pygments/popen.rb b/lib/pygments/popen.rb
index 098f734b..f04ce9e2 100644
--- a/lib/pygments/popen.rb
+++ b/lib/pygments/popen.rb
@@ -1,6 +1,6 @@
 # coding: utf-8
-require 'posix/spawn'
-require 'yajl'
+require 'open3'
+require 'multi_json'
 require 'timeout'
 require 'logger'
 require 'time'
@@ -13,9 +13,13 @@ class MentosError < IOError
 # Python process.
 module Pygments
   module Popen
-    include POSIX::Spawn
     extend self
 
+    def popen4(cmd)
+      stdin, stdout, stderr, wait_thr = Open3.popen3(cmd)
+      [wait_thr[:pid], stdin, stdout, stderr]
+    end
+
     # Get things started by opening a pipe to mentos (the freshmaker), a
     # Python process that talks to the Pygments library. We'll talk back and
     # forth across this pipe.
@@ -262,7 +266,7 @@ def mentos(method, args=[], kwargs={}, original_code=nil)
 
           kwargs.freeze
           kwargs = kwargs.merge("fd" => @out.to_i, "id" => id, "bytes" => bytesize)
-          out_header = Yajl.dump(:method => method, :args => args, :kwargs => kwargs)
+          out_header = MultiJson.dump(:method => method, :args => args, :kwargs => kwargs)
 
           # Get the size of the header itself and write that.
           bits = get_fixed_bits_from_header(out_header)
@@ -322,12 +326,12 @@ def check_for_error
     def handle_header_and_return(header, id)
       if header
         header = header_to_json(header)
-        bytes = header["bytes"]
+        bytes = header[:bytes]
 
         # Read more bytes (the actual response body)
         res = @out.read(bytes.to_i)
 
-        if header["method"] == "highlight"
+        if header[:method] == "highlight"
           # Make sure we have a result back; else consider this an error.
           if res.nil?
             @log.warn "No highlight result back from mentos."
@@ -423,7 +427,7 @@ def get_header
     # want them, text otherwise.
     def return_result(res, method)
       unless method == :lexer_name_for || method == :highlight || method == :css
-        res = Yajl.load(res, :symbolize_keys => true)
+        res = MultiJson.load(res, :symbolize_keys => true)
       end
       res = res.rstrip if res.class == String
       res
@@ -432,14 +436,14 @@ def return_result(res, method)
     # Convert a text header into JSON for easy access.
     def header_to_json(header)
       @log.info "[In header: #{header} "
-      header = Yajl.load(header)
+      header = MultiJson.load(header, :symbolize_keys => true)
 
-      if header["error"]
+      if header[:error]
         # Raise this as a Ruby exception of the MentosError class.
         # Stop so we don't leave the pipe in an inconsistent state.
         @log.error "Failed to convert header to JSON."
-        stop header["error"]
-        raise MentosError, header["error"]
+        stop header[:error]
+        raise MentosError, header[:error]
       else
         header
       end
diff --git a/pygments.rb.gemspec b/pygments.rb.gemspec
index 3f18266f..4e2f2b48 100644
--- a/pygments.rb.gemspec
+++ b/pygments.rb.gemspec
@@ -14,8 +14,7 @@ Gem::Specification.new do |s|
   s.email = ['aman@tmm1.net']
   s.license = 'MIT'
 
-  s.add_dependency 'yajl-ruby',   '~> 1.2'
-  s.add_dependency 'posix-spawn', '~> 0.3.6'
+  s.add_dependency 'multi_json', '>= 1.0.0'
   s.add_development_dependency 'rake-compiler', '~> 0.7.6'
   s.add_development_dependency 'test-unit', '~> 3.0.0'