diff --git a/Gemfile b/Gemfile
index 178f64053..d96c77701 100644
--- a/Gemfile
+++ b/Gemfile
@@ -106,7 +106,8 @@ gem 'sidekiq-statistic'
 # for sidekiq web
 gem 'sinatra', require: false
 
-gem 'therubyracer'
+gem 'execjs', github: 'rails/execjs', require: false
+gem 'mini_racer'
 gem 'thin', require: false
 gem 'highline', require: false
 gem 'rack-protection' # security
diff --git a/Gemfile.lock b/Gemfile.lock
index 5ed367706..3491b735a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,3 +1,9 @@
+GIT
+  remote: git://github.com/rails/execjs.git
+  revision: 22476229323cbec3befa8b690cc6c7c3957a0044
+  specs:
+    execjs (2.6.0)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -94,7 +100,6 @@ GEM
     erubis (2.7.0)
     eventmachine (1.2.0.1)
     excon (0.45.4)
-    execjs (2.6.0)
     exifr (1.2.4)
     fabrication (2.9.8)
     fakeweb (1.3.0)
@@ -144,7 +149,7 @@ GEM
     librarian (0.1.2)
       highline
       thor (~> 0.15)
-    libv8 (3.16.14.13)
+    libv8 (5.0.71.48.3)
     listen (0.7.3)
     logster (1.2.3)
     loofah (2.0.3)
@@ -159,6 +164,8 @@ GEM
     method_source (0.8.2)
     mime-types (2.99.1)
     mini_portile2 (2.1.0)
+    mini_racer (0.1.3)
+      libv8 (~> 5.0)
     minitest (5.8.4)
     mocha (1.1.0)
       metaclass (~> 0.0.1)
@@ -284,7 +291,6 @@ GEM
     redis (3.3.0)
     redis-namespace (1.5.2)
       redis (~> 3.0, >= 3.0.4)
-    ref (2.0.0)
     rest-client (1.8.0)
       http-cookie (>= 1.0.2, < 2.0)
       mime-types (>= 1.16, < 3.0)
@@ -373,9 +379,6 @@ GEM
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     stackprof (0.2.9)
-    therubyracer (0.12.2)
-      libv8 (~> 3.16.14.0)
-      ref
     thin (1.6.4)
       daemons (~> 1.0, >= 1.0.9)
       eventmachine (~> 1.0, >= 1.0.4)
@@ -417,6 +420,7 @@ DEPENDENCIES
   ember-rails (= 0.18.5)
   ember-source (= 1.12.2)
   excon
+  execjs!
   fabrication (= 2.9.8)
   fakeweb (~> 1.3.0)
   fast_blank
@@ -439,6 +443,7 @@ DEPENDENCIES
   memory_profiler
   message_bus (= 2.0.0.beta.11)
   mime-types
+  mini_racer
   minitest
   mocha
   mock_redis
@@ -493,7 +498,6 @@ DEPENDENCIES
   sinatra
   spork-rails
   stackprof
-  therubyracer
   thin
   timecop
   uglifier
diff --git a/app/models/site_customization.rb b/app/models/site_customization.rb
index a74e188a2..562c544f4 100644
--- a/app/models/site_customization.rb
+++ b/app/models/site_customization.rb
@@ -59,7 +59,7 @@ SCRIPT
         begin
           code = transpile(node.inner_html, node['version'])
           node.replace("<script>#{code}</script>")
-        rescue Tilt::ES6ModuleTranspilerTemplate::JavaScriptError => ex
+        rescue MiniRacer::RuntimeError => ex
           node.replace("<script type='text/discourse-js-error'>#{ex.message}</script>")
         end
       end
diff --git a/lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb b/lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb
index 58eb0e678..68b2ca990 100644
--- a/lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb
+++ b/lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb
@@ -1,22 +1,9 @@
 require 'execjs'
 require 'babel/transpiler'
+require 'mini_racer'
 
 module Tilt
 
-  class Console
-    def initialize(prefix=nil)
-      @prefix = prefix || ''
-    end
-
-    def log(msg)
-      Rails.logger.info("#{@prefix}#{msg}")
-    end
-
-    def error(msg)
-      Rails.logger.error("#{@prefix}#{msg}")
-    end
-  end
-
   class ES6ModuleTranspilerTemplate < Tilt::Template
     self.default_mime_type = 'application/javascript'
 
@@ -30,10 +17,19 @@ module Tilt
 
     def self.create_new_context
       # timeout any eval that takes longer than 15 seconds
-      ctx = V8::Context.new(timeout: 15000)
+      ctx = MiniRacer::Context.new(timeout: 15000)
       ctx.eval("var self = this; #{File.read(Babel::Transpiler.script_path)}")
       ctx.eval("module = {}; exports = {};");
       ctx.load("#{Rails.root}/lib/es6_module_transpiler/support/es6-module-transpiler.js")
+      ctx.attach("rails.logger.info", proc{|err| Rails.logger.info(err.to_s)})
+      ctx.attach("rails.logger.error", proc{|err| Rails.logger.error(err.to_s)})
+      ctx.eval <<JS
+      console = {
+        prefix: "",
+        log: function(msg){ rails.logger.info(console.prefix + msg); },
+        error: function(msg){ rails.logger.error(console.prefix + msg); }
+      }
+JS
       ctx
     end
 
@@ -60,19 +56,9 @@ module Tilt
     end
 
     def self.protect
-      rval = nil
       @mutex.synchronize do
-        begin
-          rval = yield
-          # This may seem a bit odd, but we don't want to leak out
-          # objects that require locks on the v8 vm, to get a backtrace
-          # you need a lock, if this happens in the wrong spot you can
-          # deadlock a process
-        rescue V8::Error => e
-          raise JavaScriptError.new(e.message, e.backtrace)
-        end
+        yield
       end
-      rval
     end
 
     def whitelisted?(path)
@@ -98,7 +84,7 @@ module Tilt
     def babel_transpile(source)
       klass = self.class
       klass.protect do
-        klass.v8['console'] = Console.new("BABEL: babel-eval: ")
+        klass.v8.eval("console.prefix = 'BABEL: babel-eval: ';")
         @output = klass.v8.eval(babel_source(source))
       end
     end
@@ -108,7 +94,7 @@ module Tilt
 
       klass = self.class
       klass.protect do
-        klass.v8['console'] = Console.new("BABEL: #{scope.logical_path}: ")
+        klass.v8.eval("console.prefix = 'BABEL: #{scope.logical_path}: ';")
         @output = klass.v8.eval(generate_source(scope))
       end
 
diff --git a/lib/js_locale_helper.rb b/lib/js_locale_helper.rb
index db4821a37..eb2f1a19d 100644
--- a/lib/js_locale_helper.rb
+++ b/lib/js_locale_helper.rb
@@ -154,15 +154,25 @@ module JsLocaleHelper
     result
   end
 
-  def self.compile_message_format(locale, format)
-    ctx = V8::Context.new
-    ctx.load(Rails.root + 'lib/javascripts/messageformat.js')
-    path = Rails.root + "lib/javascripts/locale/#{locale}.js"
-    ctx.load(path) if File.exists?(path)
-    ctx.eval("mf = new MessageFormat('#{locale}');")
-    ctx.eval("mf.precompile(mf.parse(#{format.inspect}))")
+  @mutex = Mutex.new
+  def self.with_context
+    @mutex.synchronize do
+      yield @ctx ||= begin
+               ctx = MiniRacer::Context.new
+               ctx.load(Rails.root + 'lib/javascripts/messageformat.js')
+               ctx
+             end
+    end
+  end
 
-  rescue V8::Error => e
+  def self.compile_message_format(locale, format)
+    with_context do |ctx|
+      path = Rails.root + "lib/javascripts/locale/#{locale}.js"
+      ctx.load(path) if File.exists?(path)
+      ctx.eval("mf = new MessageFormat('#{locale}');")
+      ctx.eval("mf.precompile(mf.parse(#{format.inspect}))")
+    end
+  rescue MiniRacer::EvalError => e
     message = "Invalid Format: " << e.message
     "function(){ return #{message.inspect};}"
   end
diff --git a/lib/pretty_text.rb b/lib/pretty_text.rb
index e3e5cc756..b328f230f 100644
--- a/lib/pretty_text.rb
+++ b/lib/pretty_text.rb
@@ -1,4 +1,4 @@
-require 'v8'
+require 'mini_racer'
 require 'nokogiri'
 require_dependency 'url_helper'
 require_dependency 'excerpt_parser'
@@ -7,7 +7,9 @@ require_dependency 'discourse_tagging'
 
 module PrettyText
 
-  class Helpers
+  module Helpers
+    extend self
+
     def t(key, opts)
       key = "js." + key
       unless opts
@@ -81,6 +83,7 @@ module PrettyText
         nil
       end
     end
+
   end
 
   @mutex = Mutex.new
@@ -92,9 +95,11 @@ module PrettyText
 
   def self.create_new_context
     # timeout any eval that takes longer than 15 seconds
-    ctx = V8::Context.new(timeout: 15000)
+    ctx = MiniRacer::Context.new(timeout: 15000)
 
-    ctx["helpers"] = Helpers.new
+    Helpers.instance_methods.each do |method|
+      ctx.attach("helpers.#{method}", Helpers.method(method))
+    end
 
     ctx_load(ctx,
       "vendor/assets/javascripts/md5.js",
@@ -198,6 +203,7 @@ module PrettyText
     # we use the exact same markdown converter as the client
     # TODO: use the same extensions on both client and server (in particular the template for mentions)
     baked = nil
+    text = text || ""
 
     protect do
       context = v8
@@ -206,8 +212,9 @@ module PrettyText
 
       context_opts = opts || {}
       context_opts[:sanitize] = true unless context_opts[:sanitize] == false
-      context['opts'] = context_opts
-      context['raw'] = text
+
+      context.eval("opts = #{context_opts.to_json};")
+      context.eval("raw = #{text.inspect};")
 
       if Post.white_listed_image_classes.present?
         Post.white_listed_image_classes.each do |klass|
@@ -258,8 +265,10 @@ module PrettyText
   # leaving this here, cause it invokes v8, don't want to implement twice
   def self.avatar_img(avatar_template, size)
     protect do
-      v8['avatarTemplate'] = avatar_template
-      v8['size'] = size
+      v8.eval <<JS
+      avatarTemplate = #{avatar_template.inspect};
+      size = #{size.to_i};
+JS
       decorate_context(v8)
       v8.eval("Discourse.Utilities.avatarImg({ avatarTemplate: avatarTemplate, size: size });")
     end
@@ -267,9 +276,8 @@ module PrettyText
 
   def self.unescape_emoji(title)
     protect do
-      v8["title"] = title
       decorate_context(v8)
-      v8.eval("Discourse.Emoji.unescape(title)")
+      v8.eval("Discourse.Emoji.unescape(#{title.inspect})")
     end
   end
 
@@ -413,15 +421,7 @@ module PrettyText
   def self.protect
     rval = nil
     @mutex.synchronize do
-      begin
-        rval = yield
-        # This may seem a bit odd, but we don't want to leak out
-        # objects that require locks on the v8 vm, to get a backtrace
-        # you need a lock, if this happens in the wrong spot you can
-        # deadlock a process
-      rescue V8::Error => e
-        raise JavaScriptError.new(e.message, e.backtrace)
-      end
+      rval = yield
     end
     rval
   end
diff --git a/spec/components/js_locale_helper_spec.rb b/spec/components/js_locale_helper_spec.rb
index 1b26efe88..125474f93 100644
--- a/spec/components/js_locale_helper_spec.rb
+++ b/spec/components/js_locale_helper_spec.rb
@@ -1,5 +1,6 @@
 require 'rails_helper'
 require_dependency 'js_locale_helper'
+require 'mini_racer'
 
 describe JsLocaleHelper do
 
@@ -25,7 +26,7 @@ describe JsLocaleHelper do
   end
 
   def setup_message_format(format)
-    @ctx = V8::Context.new
+    @ctx = MiniRacer::Context.new
     @ctx.eval('MessageFormat = {locale: {}};')
     @ctx.load(Rails.root + 'lib/javascripts/locale/en.js')
     compiled = JsLocaleHelper.compile_message_format('en', format)
@@ -72,7 +73,7 @@ describe JsLocaleHelper do
   end
 
   it 'handles message format special keys' do
-    ctx = V8::Context.new
+    ctx = MiniRacer::Context.new
     ctx.eval("I18n = {};")
 
     JsLocaleHelper.set_translations 'en', {
@@ -149,7 +150,7 @@ describe JsLocaleHelper do
     SiteSetting.default_locale = 'ru'
     I18n.locale = :uk
 
-    ctx = V8::Context.new
+    ctx = MiniRacer::Context.new
     ctx.eval('var window = this;')
     ctx.load(Rails.root + 'app/assets/javascripts/locales/i18n.js')
     ctx.eval(JsLocaleHelper.output_locale(I18n.locale))
@@ -167,7 +168,7 @@ describe JsLocaleHelper do
   LocaleSiteSetting.values.each do |locale|
     it "generates valid date helpers for #{locale[:value]} locale" do
       js = JsLocaleHelper.output_locale(locale[:value])
-      ctx = V8::Context.new
+      ctx = MiniRacer::Context.new
       ctx.eval('var window = this;')
       ctx.load(Rails.root + 'app/assets/javascripts/locales/i18n.js')
       ctx.eval(js)