diff --git a/actionpack/lib/action_dispatch.rb b/actionpack/lib/action_dispatch.rb
index dcd3ee0644..74ddf2954a 100644
--- a/actionpack/lib/action_dispatch.rb
+++ b/actionpack/lib/action_dispatch.rb
@@ -53,6 +53,7 @@ module ActionDispatch
     autoload :ExceptionWrapper
     autoload :Flash
     autoload :ParamsParser
+    autoload :ApiPublicExceptions
     autoload :PublicExceptions
     autoload :Reloader
     autoload :RemoteIp
diff --git a/actionpack/lib/action_dispatch/middleware/api_public_exceptions.rb b/actionpack/lib/action_dispatch/middleware/api_public_exceptions.rb
new file mode 100644
index 0000000000..126842672d
--- /dev/null
+++ b/actionpack/lib/action_dispatch/middleware/api_public_exceptions.rb
@@ -0,0 +1,47 @@
+module ActionDispatch
+  class ApiPublicExceptions
+    attr_accessor :public_path
+
+    def initialize(public_path)
+      @public_path = public_path
+    end
+
+    def call(env)
+      exception    = env["action_dispatch.exception"]
+      status       = env["PATH_INFO"][1..-1]
+      request      = ActionDispatch::Request.new(env)
+      content_type = request.formats.first
+      body         = { :status => status, :error => exception.message }
+
+      render(status, content_type, body)
+    end
+
+    private
+
+    def render(status, content_type, body)
+      format = content_type && "to_#{content_type.to_sym}"
+      if format && body.respond_to?(format)
+        render_format(status, content_type, body.public_send(format))
+      else
+        render_html(status)
+      end
+    end
+
+    def render_format(status, content_type, body)
+      [status, {'Content-Type' => "#{content_type}; charset=#{ActionDispatch::Response.default_charset}",
+                'Content-Length' => body.bytesize.to_s}, [body]]
+    end
+
+    def render_html(status)
+      found = false
+      path = "#{public_path}/#{status}.#{I18n.locale}.html" if I18n.locale
+      path = "#{public_path}/#{status}.html" unless path && (found = File.exist?(path))
+
+      if found || File.exist?(path)
+        render_format(status, 'text/html', File.read(path))
+      else
+        [404, { "X-Cascade" => "pass" }, []]
+      end
+    end
+  end
+end
diff --git a/actionpack/test/dispatch/show_exceptions_test.rb b/actionpack/test/dispatch/show_exceptions_test.rb
index 72eaa916bc..c70bc5f95e 100644
--- a/actionpack/test/dispatch/show_exceptions_test.rb
+++ b/actionpack/test/dispatch/show_exceptions_test.rb
@@ -11,7 +11,7 @@ class ShowExceptionsTest < ActionDispatch::IntegrationTest
       when "/bad_params"
         raise ActionDispatch::ParamsParser::ParseError.new("", StandardError.new)
       when "/method_not_allowed"
-        raise ActionController::MethodNotAllowed
+        raise ActionController::MethodNotAllowed, 'PUT'
       when "/unknown_http_method"
         raise ActionController::UnknownHttpMethod
       when "/not_found_original_exception"
@@ -22,7 +22,8 @@ class ShowExceptionsTest < ActionDispatch::IntegrationTest
     end
   end
 
-  ProductionApp = ActionDispatch::ShowExceptions.new(Boomer.new, ActionDispatch::PublicExceptions.new("#{FIXTURE_LOAD_PATH}/public"))
+  ProductionApp    = ActionDispatch::ShowExceptions.new(Boomer.new, ActionDispatch::PublicExceptions.new("#{FIXTURE_LOAD_PATH}/public"))
+  ProductionApiApp = ActionDispatch::ShowExceptions.new(Boomer.new, ActionDispatch::ApiPublicExceptions.new("#{FIXTURE_LOAD_PATH}/public"))
 
   test "skip exceptions app if not showing exceptions" do
     @app = ProductionApp
@@ -55,6 +56,42 @@ class ShowExceptionsTest < ActionDispatch::IntegrationTest
     assert_equal "", body
   end
 
+  test "rescue api apps with json response" do
+    @app = ProductionApiApp
+
+    get "/", headers: { 'HTTP_ACCEPT' => 'application/json', 'action_dispatch.show_exceptions' => true }
+    assert_response 500
+    assert_equal({ :status => '500', :error => 'puke!' }.to_json, body)
+
+    get "/method_not_allowed", headers: { 'HTTP_ACCEPT' => 'application/json', 'action_dispatch.show_exceptions' => true }
+    assert_response 405
+    assert_equal({ :status => '405', :error => 'Only PUT requests are allowed.' }.to_json, body)
+
+    get "/unknown_http_method", headers: { 'HTTP_ACCEPT' => 'application/json', 'action_dispatch.show_exceptions' => true }
+    assert_response 405
+    assert_equal({ :status => '405', :error => 'ActionController::UnknownHttpMethod' }.to_json, body)
+  end
+
+  test "rescue api apps unknown content-type requests with html response" do
+    @app = ProductionApiApp
+
+    get "/", headers: { 'HTTP_ACCEPT' => 'application/x-custom', 'action_dispatch.show_exceptions' => true }
+    assert_response 500
+    assert_equal "500 error fixture\n", body
+
+    get "/bad_params", headers: { 'HTTP_ACCEPT' => 'application/x-custom', 'action_dispatch.show_exceptions' => true }
+    assert_response 400
+    assert_equal "400 error fixture\n", body
+
+    get "/not_found", headers: { 'HTTP_ACCEPT' => 'application/x-custom', 'action_dispatch.show_exceptions' => true }
+    assert_response 404
+    assert_equal "404 error fixture\n", body
+
+    get "/unknown_http_method", headers: { 'HTTP_ACCEPT' => 'application/x-custom', 'action_dispatch.show_exceptions' => true }
+    assert_response 405
+    assert_equal("", body)
+  end
+
   test "localize rescue error page" do
     old_locale, I18n.locale = I18n.locale, :da