diff --git a/.travis.yml b/.travis.yml
index 5b8b888..6f9fab0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,12 +9,17 @@ gemfile:
   - gemfiles/sprockets_rails_2_with_sprockets_2.gemfile
   - gemfiles/sprockets_rails_2_with_sprockets_3.gemfile
   - gemfiles/sprockets_rails_3_with_sprockets_3.gemfile
+  - gemfiles/sprockets_rails_3_with_sprockets_4.gemfile
 matrix:
   exclude:
     - rvm: 2.0
       gemfile: gemfiles/sprockets_rails_3_with_sprockets_3.gemfile
     - rvm: 2.1.9
       gemfile: gemfiles/sprockets_rails_3_with_sprockets_3.gemfile
+    - rvm: 2.0
+      gemfile: gemfiles/sprockets_rails_3_with_sprockets_4.gemfile
+    - rvm: 2.1.9
+      gemfile: gemfiles/sprockets_rails_3_with_sprockets_4.gemfile
 branches:
   only:
     - master
diff --git a/Appraisals b/Appraisals
index 71f2fbe..f24e99f 100644
--- a/Appraisals
+++ b/Appraisals
@@ -20,3 +20,8 @@ appraise "sprockets-rails 3 with sprockets 3" do
   gem "sprockets-rails", "~> 3.0"
   gem "sprockets", "~> 3.0"
 end
+
+appraise "sprockets-rails 3 with sprockets 4" do
+  gem "sprockets-rails", "~> 3.0"
+  gem "sprockets", "~> 4.0.0.beta1"
+end
diff --git a/README.md b/README.md
index af68ed2..bb5af9f 100644
--- a/README.md
+++ b/README.md
@@ -64,14 +64,14 @@ This will generate `public/404.html`.
 
 ## Template engines
 Gakubuchi supports some template engines: `ERB`, `Haml` and `Slim`.  
-If you want to use `Haml` or `Slim`, you need to put them in your Gemfile:
+When you want to use `Haml` or `Slim`, you need to put them in your Gemfile:
 
 ```ruby
 # Use Haml
-gem 'haml-rails'
+gem 'haml'
 
 # Use Slim
-gem 'slim-rails'
+gem 'slim'
 ```
 
 ## Using assets
@@ -123,7 +123,7 @@ bundle install
 appraisal install
 
 # Run RSpec with a specific combination
-appraisal 'sprockets-rails 3 with sprockets 3' rspec
+appraisal 'sprockets-rails 3 with sprockets 4' rspec
 
 # Run RSpec with all combinations
 appraisal rspec
diff --git a/gakubuchi.gemspec b/gakubuchi.gemspec
index 3fb225c..7703f0a 100644
--- a/gakubuchi.gemspec
+++ b/gakubuchi.gemspec
@@ -14,9 +14,10 @@ Gem::Specification.new do |s|
   s.description = "Gakubuchi provides a simple way to manage static pages with Asset Pipeline."
   s.license     = "MIT"
 
-  s.required_ruby_version = '>= 2.0.0'
+  s.required_ruby_version = ">= 2.0.0"
   s.files = Dir["lib/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
 
+  s.add_dependency "grease", "~> 0.3.0"
   s.add_dependency "railties", ">= 4.0.0"
   s.add_dependency "sprockets-rails", ">= 2.0.0"
 
@@ -28,6 +29,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "rspec-rails", ">= 3.0.1"
   s.add_development_dependency "rubocop"
   s.add_development_dependency "simplecov"
-  s.add_development_dependency "slim-rails"
+  # TODO: Deal with the bugs on the latest version of slim-rails
+  s.add_development_dependency "slim-rails", "< 3.1.1"
   s.add_development_dependency "sqlite3"
 end
diff --git a/gemfiles/sprockets_rails_3_with_sprockets_4.gemfile b/gemfiles/sprockets_rails_3_with_sprockets_4.gemfile
new file mode 100644
index 0000000..ee91bf3
--- /dev/null
+++ b/gemfiles/sprockets_rails_3_with_sprockets_4.gemfile
@@ -0,0 +1,13 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "sprockets-rails", "~> 3.0"
+gem "sprockets", "~> 4.0.0.beta1"
+
+group :development, :test do
+  gem "pry-byebug"
+  gem "pry-coolline"
+end
+
+gemspec :path => "../"
diff --git a/lib/gakubuchi.rb b/lib/gakubuchi.rb
index f0fad92..855b2a6 100644
--- a/lib/gakubuchi.rb
+++ b/lib/gakubuchi.rb
@@ -6,6 +6,7 @@
 require "gakubuchi/configuration"
 require "gakubuchi/error"
 require "gakubuchi/fileutils"
+require "gakubuchi/mime_type"
 require "gakubuchi/task"
 require "gakubuchi/version"
 
diff --git a/lib/gakubuchi/engine_registrar.rb b/lib/gakubuchi/engine_registrar.rb
index 5a71b44..9dcdde1 100644
--- a/lib/gakubuchi/engine_registrar.rb
+++ b/lib/gakubuchi/engine_registrar.rb
@@ -1,30 +1,53 @@
+require "active_support/inflector"
+require "grease"
+require "sprockets"
+
 module Gakubuchi
   class EngineRegistrar
+    EXTENSION_WITH_SIGLE_DOT = /\A\.[^\.]+\z/
+
     def initialize(env)
       @env = env
     end
 
-    def register(target, engine)
-      klass = constantize(engine)
-      return false if !klass.instance_of?(::Class) || registered?(target)
+    def register(mime_type, engine_name_or_class)
+      engine = constantize(engine_name_or_class)
+      return false if !engine.instance_of?(::Class) || mime_type.extensions.empty?
 
-      args = [target, klass]
-      args << { silence_deprecation: true } if Sprockets::VERSION.start_with?("3")
+      if sprockets_major_version >= 4
+        register_as_transformer(mime_type, engine)
+      else
+        register_as_engine(mime_type, engine)
+      end
 
-      @env.register_engine(*args)
       true
     end
 
-    def registered?(target)
-      @env.engines.key?(::Sprockets::Utils.normalize_extension(target))
-    end
-
     private
 
-    def constantize(klass)
-      klass.to_s.constantize
+    def constantize(constant_name)
+      constant_name.to_s.constantize
     rescue ::LoadError, ::NameError
       nil
     end
+
+    def sprockets_major_version
+      @sprockets_major_version ||= ::Gem::Version.new(::Sprockets::VERSION).segments.first
+    end
+
+    def register_as_engine(mime_type, engine)
+      mime_type.extensions.select { |ext| ext =~ EXTENSION_WITH_SIGLE_DOT }.each do |ext|
+        args = [ext, engine]
+        args << { silence_deprecation: true } if sprockets_major_version == 3
+        @env.register_engine(*args)
+      end
+    end
+
+    def register_as_transformer(mime_type, engine)
+      content_type = mime_type.content_type
+
+      @env.register_mime_type(content_type, extensions: mime_type.extensions)
+      @env.register_transformer(content_type, engine.default_mime_type, ::Grease.apply(engine))
+    end
   end
 end
diff --git a/lib/gakubuchi/error.rb b/lib/gakubuchi/error.rb
index 75e5160..0f3a49c 100644
--- a/lib/gakubuchi/error.rb
+++ b/lib/gakubuchi/error.rb
@@ -1,5 +1,6 @@
 module Gakubuchi
   class Error < StandardError
     InvalidTemplate = Class.new(self)
+    InvalidMimeType = Class.new(self)
   end
 end
diff --git a/lib/gakubuchi/mime_type.rb b/lib/gakubuchi/mime_type.rb
new file mode 100644
index 0000000..cf26f20
--- /dev/null
+++ b/lib/gakubuchi/mime_type.rb
@@ -0,0 +1,20 @@
+require "gakubuchi/error"
+require "set"
+
+module Gakubuchi
+  class MimeType
+    CONTENT_TYPE_FORMAT = %r(\A[^/]+/[^/]+\z)
+
+    attr_reader :content_type, :extensions
+
+    def initialize(content_type, extensions: [])
+      unless content_type =~ CONTENT_TYPE_FORMAT
+        message = %(`#{content_type}' is invalid as Content-Type)
+        raise ::Gakubuchi::Error::InvalidMimeType, message
+      end
+
+      @content_type = content_type
+      @extensions = ::Set.new(extensions).map(&:to_s)
+    end
+  end
+end
diff --git a/lib/gakubuchi/railtie.rb b/lib/gakubuchi/railtie.rb
index db70db1..ab90e43 100644
--- a/lib/gakubuchi/railtie.rb
+++ b/lib/gakubuchi/railtie.rb
@@ -3,8 +3,17 @@ class Railtie < ::Rails::Railtie
     config.assets.configure do |env|
       engine_registrar = EngineRegistrar.new(env)
 
-      engine_registrar.register(:haml, "::Tilt::HamlTemplate")
-      engine_registrar.register(:slim, "::Slim::Template")
+      haml = ::Gakubuchi::MimeType.new("text/haml", extensions: %w(.haml .html.haml))
+      engine_registrar.register(haml, "Tilt::HamlTemplate")
+
+      slim = ::Gakubuchi::MimeType.new("text/slim", extensions: %w(.slim .html.slim))
+      engine_registrar.register(slim, "Slim::Template")
+    end
+
+    config.after_initialize do
+      # NOTE: Call #to_s for Sprockets 4 or later
+      templates = ::Gakubuchi::Template.all.map { |template| template.logical_path.to_s }
+      config.assets.precompile += templates
     end
 
     rake_tasks do
diff --git a/lib/gakubuchi/template.rb b/lib/gakubuchi/template.rb
index 877a45a..c7c643e 100644
--- a/lib/gakubuchi/template.rb
+++ b/lib/gakubuchi/template.rb
@@ -39,7 +39,8 @@ def destination_path
     end
 
     def digest_path
-      asset = assets.find_asset(logical_path)
+      # NOTE: Call #to_s for Sprockets 4 or later
+      asset = assets.find_asset(logical_path.to_s)
       return if asset.nil?
 
       ::Pathname.new(::File.join(::Rails.public_path, app.config.assets.prefix, asset.digest_path))
diff --git a/spec/dummy/app/assets/config/manifest.js b/spec/dummy/app/assets/config/manifest.js
new file mode 100644
index 0000000..b16e53d
--- /dev/null
+++ b/spec/dummy/app/assets/config/manifest.js
@@ -0,0 +1,3 @@
+//= link_tree ../images
+//= link_directory ../javascripts .js
+//= link_directory ../stylesheets .css
diff --git a/spec/dummy/app/assets/images/.keep b/spec/dummy/app/assets/images/.keep
new file mode 100644
index 0000000..e69de29
diff --git a/spec/lib/gakubuchi/engine_registrar_spec.rb b/spec/lib/gakubuchi/engine_registrar_spec.rb
index fc6d85b..e55f543 100644
--- a/spec/lib/gakubuchi/engine_registrar_spec.rb
+++ b/spec/lib/gakubuchi/engine_registrar_spec.rb
@@ -1,71 +1,68 @@
 require "rails_helper"
 
 RSpec.describe Gakubuchi::EngineRegistrar do
-  let(:env) { Sprockets::Environment.new }
   let(:engine_registrar) { described_class.new(env) }
+  let(:env) { Sprockets::Environment.new }
 
   describe "#register" do
-    let(:described_method) { -> { engine_registrar.register(target, engine) } }
+    let(:described_method) { -> { engine_registrar.register(mime_type, engine) } }
+    let(:mime_type) { Gakubuchi::MimeType.new(content_type, extensions: extensions) }
+    let(:sprokcets_extensions) do
+      extension_type = major_version_of(Sprockets) >= 4 ? :transformers : :engines
+      -> { env.public_send(extension_type) }
+    end
 
     context "when specified engine is an uninitialized constant" do
-      let(:target) { :foo }
+      let(:content_type) { "application/csv+ruby" }
       let(:engine) { "Foo" }
+      let(:extensions) { %w(.rcsv .csv.ruby) }
 
-      describe "env.engines" do
-        subject { -> { env.engines } }
-        it { expect(&described_method).not_to change(&subject) }
+      it "should return false" do
+        expect(described_method.call).to eq false
       end
 
-      describe "return value" do
-        subject { described_method.call }
-        it { is_expected.to eq false }
+      it "shouldn't register the engine for the MIME type" do
+        expect(&described_method).not_to change(&sprokcets_extensions)
       end
     end
 
-    context "when specified target is already registered" do
-      let(:target) { :sass }
-      let(:engine) { "Sprockets::SassTemplate" }
+    context "when there is no extensions corresponding the MIME type" do
+      let(:content_type) { "application/csv+ruby" }
+      let(:engine) { Tilt::CSVTemplate }
+      let(:extensions) { nil }
 
-      describe "env.engines" do
-        subject { -> { env.engines } }
-        it { expect(&described_method).not_to change(&subject) }
+      it "should return false" do
+        expect(described_method.call).to eq false
       end
 
-      describe "return value" do
-        subject { described_method.call }
-        it { is_expected.to eq false }
+      it "shouldn't register the engine for the MIME type" do
+        expect(&described_method).not_to change(&sprokcets_extensions)
       end
     end
 
-    context "when specified target is not registered" do
-      let(:target) { :foo }
-      let(:engine) { "Sprockets::SassTemplate" }
+    context "when all parameters are valid" do
+      let(:content_type) { "application/csv+ruby" }
+      let(:engine) { Tilt::CSVTemplate }
+      let(:extensions) { %w(.rcsv .csv.ruby) }
+      let(:extensions_with_single_dot) { extensions.select { |ext| ext =~ /\A\.[^\.]+\z/ } }
 
-      describe "env.engines" do
-        subject { -> { env.engines } }
-        let(:expectation) { a_hash_including(".foo" => Sprockets::SassTemplate) }
-
-        it { expect(&described_method).to change(&subject).to(expectation) }
+      it "should return true" do
+        expect(described_method.call).to eq true
       end
 
-      describe "return value" do
-        subject { described_method.call }
-        it { is_expected.to eq true }
-      end
-    end
-  end
-
-  describe "#registered?" do
-    subject { engine_registrar.registered?(target) }
+      it "should register the engine for the MIME type" do
+        diff =
+          case major_version_of(Sprockets)
+          when 2
+            Hash[extensions_with_single_dot.map { |ext| [ext, engine] }]
+          when 3
+            Hash[extensions_with_single_dot.map { |ext| [ext, an_object_responding_to(:call)] }]
+          when 4..Float::INFINITY
+            { content_type => { engine.default_mime_type => an_object_responding_to(:call) } }
+          end
 
-    context "when specified target is not registered" do
-      let(:target) { :foo }
-      it { is_expected.to eq false }
-    end
-
-    context "when specified target is already registered" do
-      let(:target) { :erb }
-      it { is_expected.to eq true }
+        expect(&described_method).to change(&sprokcets_extensions).to(hash_including(diff))
+      end
     end
   end
 end
diff --git a/spec/lib/gakubuchi/mime_type_spec.rb b/spec/lib/gakubuchi/mime_type_spec.rb
new file mode 100644
index 0000000..e1107b9
--- /dev/null
+++ b/spec/lib/gakubuchi/mime_type_spec.rb
@@ -0,0 +1,49 @@
+require "rails_helper"
+
+RSpec.describe Gakubuchi::MimeType do
+  describe "#new" do
+    subject { -> { described_class.new(content_type) } }
+
+    context "when an invalid `content_type` is specified" do
+      let(:content_type) { "foo" }
+      it { is_expected.to raise_error(Gakubuchi::Error::InvalidMimeType, /#{content_type}/) }
+    end
+
+    context "when a valid `content_type` is specified" do
+      let(:content_type) { "application/csv+ruby" }
+      it { is_expected.not_to raise_error }
+    end
+  end
+
+  describe "#content_type" do
+    subject { described_class.new(content_type).content_type }
+    let(:content_type) { "application/csv+ruby" }
+
+    it { is_expected.to eq content_type }
+  end
+
+  describe "#extensions" do
+    subject { described_class.new("application/csv+ruby", options).extensions }
+
+    context "when `extensions` isn't specified" do
+      let(:options) { { extensions: nil } }
+
+      it { is_expected.to be_an_instance_of(Array) }
+      it { is_expected.to be_empty }
+    end
+
+    context "when `extensions` includes duplicated values" do
+      let(:options) { { extensions: %w(.rcsv .csv.ruby .rcsv) } }
+
+      it { is_expected.to be_an_instance_of(Array) }
+      it { is_expected.to contain_exactly(*options[:extensions].uniq) }
+    end
+
+    context "when `extensions` includes non-string values" do
+      let(:options) { { extensions: %i(.rcsv .csv.ruby) } }
+
+      it { is_expected.to be_an_instance_of(Array) }
+      it { is_expected.to contain_exactly(*options[:extensions].map(&:to_s)) }
+    end
+  end
+end
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index 2884feb..5a8d566 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -28,13 +28,16 @@
 # directory. Alternatively, in the individual `*_spec.rb` files, manually
 # require only the support files necessary.
 #
-# Dir[Rails.root.join('spec/support/**/*.rb')].each { |f| require f }
+Dir[File.expand_path("../../spec/support/**/*.rb", __FILE__)].each { |f| require f }
 
 # Checks for pending migrations before tests are run.
 # If you are not using ActiveRecord, you can remove this line.
 # ActiveRecord::Migration.maintain_test_schema!
 
 RSpec.configure do |config|
+  # Include modules in all example groups
+  config.include VersionHelpers
+
   # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
   config.fixture_path = "#{::Rails.root}/spec/fixtures"
 
diff --git a/spec/support/version_helpers.rb b/spec/support/version_helpers.rb
new file mode 100644
index 0000000..bf85266
--- /dev/null
+++ b/spec/support/version_helpers.rb
@@ -0,0 +1,7 @@
+module VersionHelpers
+  module_function
+
+  def major_version_of(mod)
+    Gem::Version.new(mod::VERSION).segments.first
+  end
+end