diff --git a/actionpack/lib/abstract_controller/rendering.rb b/actionpack/lib/abstract_controller/rendering.rb
index eec7e520fa..402ad7c8d7 100644
--- a/actionpack/lib/abstract_controller/rendering.rb
+++ b/actionpack/lib/abstract_controller/rendering.rb
@@ -76,7 +76,7 @@ module AbstractController
     # :api: plugin
     def render_to_string(options={})
       _normalize_options(options)
-      AbstractController::Rendering.body_to_s(render_to_body(options))
+      render_to_body(options)
     end
 
     # Find and renders a template based on the options given.
@@ -90,18 +90,6 @@ module AbstractController
       controller_path
     end
 
-    # Return a string representation of a Rack-compatible response body.
-    def self.body_to_s(body)
-      if body.respond_to?(:to_str)
-        body
-      else
-        strings = []
-        body.each { |part| strings << part.to_s }
-        body.close if body.respond_to?(:close)
-        strings.join
-      end
-    end
-
   private
 
     # This method should return a hash with assigns.
diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index a148c19a31..30aa34d956 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -38,7 +38,8 @@ module ActionController
     delegate :session, :to => "@_request"
 
     def initialize(*)
-      @_headers = {}
+      @_headers = {"Content-Type" => "text/html"}
+      @_status = 200
       super
     end
 
@@ -70,6 +71,11 @@ module ActionController
       @_status = Rack::Utils.status_code(status)
     end
 
+    def response_body=(val)
+      body = val.respond_to?(:each) ? val : [val]
+      super body
+    end
+
     # :api: private
     def dispatch(name, request)
       @_request = request
diff --git a/actionpack/test/controller/new_base/bare_metal_test.rb b/actionpack/test/controller/new_base/bare_metal_test.rb
new file mode 100644
index 0000000000..df4b39a103
--- /dev/null
+++ b/actionpack/test/controller/new_base/bare_metal_test.rb
@@ -0,0 +1,27 @@
+require "abstract_unit"
+
+module BareMetalTest
+  class BareController < ActionController::Metal
+    def index
+      self.response_body = "Hello world"
+    end
+  end
+
+  class BareTest < ActiveSupport::TestCase
+    test "response body is a Rack-compatible response" do
+      status, headers, body = BareController.action(:index).call(Rack::MockRequest.env_for("/"))
+      assert_equal 200, status
+      string = ""
+
+      body.each do |part|
+        assert part.is_a?(String), "Each part of the body must be a String"
+        string << part
+      end
+
+      assert headers.is_a?(Hash), "Headers must be a Hash"
+      assert headers["Content-Type"], "Content-Type must exist"
+
+      assert_equal "Hello world", string
+    end
+  end
+end
\ No newline at end of file