diff --git a/CHANGELOG.rdoc b/CHANGELOG.rdoc
index 2e2ddceb..0376ed74 100644
--- a/CHANGELOG.rdoc
+++ b/CHANGELOG.rdoc
@@ -5,6 +5,7 @@
 * enhancements
   * Added OAuth 2 support
   * sign_out_via is available in the router to configure the method used for sign out (by github.com/martinrehfeld)
+  * Improved Ajax requests handling in failure app (by github.com/spastorino)
 
 * bugfix
   * after_sign_in_path_for always receives a resource
diff --git a/lib/devise/failure_app.rb b/lib/devise/failure_app.rb
index 4705f108..e253f54e 100644
--- a/lib/devise/failure_app.rb
+++ b/lib/devise/failure_app.rb
@@ -33,7 +33,7 @@ module Devise
 
     def http_auth
       self.status = 401
-      self.headers["WWW-Authenticate"] = %(Basic realm=#{Devise.http_authentication_realm.inspect}) unless request.xhr?
+      self.headers["WWW-Authenticate"] = %(Basic realm=#{Devise.http_authentication_realm.inspect}) if http_auth_header?
       self.content_type = request.format.to_s
       self.response_body = http_auth_body
     end
@@ -67,6 +67,14 @@ module Devise
       send(:"new_#{scope}_session_path")
     end
 
+    # Choose whether we should respond in a http authentication fashion,
+    # including 401 and optional headers.
+    #
+    # This method allows the user to explicitly disable http authentication
+    # on ajax requests in case they want to redirect on failures instead of
+    # handling the errors on their own. This is useful in case your ajax API
+    # is the same as your public API and uses a format like JSON (so you
+    # cannot mark JSON as a navigational format).
     def http_auth?
       if request.xhr?
         Devise.http_authenticatable_on_xhr
@@ -75,6 +83,12 @@ module Devise
       end
     end
 
+    # It does not make sense to send authenticate headers in ajax requests
+    # or if the user disabled them.
+    def http_auth_header?
+      Devise.mappings[scope].to.http_authenticatable && !request.xhr?
+    end
+
     def http_auth_body
       method = :"to_#{request.format.to_sym}"
       {}.respond_to?(method) ? { :error => i18n_message }.send(method) : i18n_message
diff --git a/test/failure_app_test.rb b/test/failure_app_test.rb
index a614d8ed..86a8c681 100644
--- a/test/failure_app_test.rb
+++ b/test/failure_app_test.rb
@@ -17,7 +17,7 @@ class FailureTest < ActiveSupport::TestCase
       'rack.input' => "",
       'warden' => OpenStruct.new(:message => nil)
     }.merge!(env_params)
-    
+
     @response = Devise::FailureApp.call(env).to_a
     @request  = ActionDispatch::Request.new(env)
   end
@@ -72,48 +72,65 @@ class FailureTest < ActiveSupport::TestCase
       assert_equal 401, @response.first
     end
 
-    test 'return WWW-authenticate headers' do
+    test 'return WWW-authenticate headers if model allows' do
       call_failure('formats' => :xml)
       assert_equal 'Basic realm="Application"', @response.second["WWW-Authenticate"]
     end
 
-    test 'dont return WWW-authenticate on ajax call if http_authenticatable_on_xhr false' do
-      swap Devise, :http_authenticatable_on_xhr => false do
-        call_failure('formats' => :html, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
-        assert_equal 302, @response.first
-        assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
-        assert_nil @response.second['WWW-Authenticate']
+    test 'does not return WWW-authenticate headers if model does not allow' do
+      swap Devise, :http_authenticatable => false do
+        call_failure('formats' => :xml)
+        assert_nil @response.second["WWW-Authenticate"]
       end
     end
 
-    test 'dont return WWW-authenticate on ajax call with formats => json if http_authenticatable_on_xhr false' do
-      swap Devise, :http_authenticatable_on_xhr => false do
-        call_failure('formats' => :json, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
-        assert_equal 302, @response.first
-        assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
-        assert_nil @response.second['WWW-Authenticate']
-      end
-    end
-
-    test 'return WWW-authenticate on ajax call if http_authenticatable_on_xhr true' do
-      swap Devise, :http_authenticatable_on_xhr => true do
-        call_failure('formats' => :html, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
-        assert_equal 401, @response.first
-        assert_nil @response.second['WWW-Authenticate']
-      end
-    end
-    
-    test 'uses the proxy failure message as response body' do
-      call_failure('formats' => :xml, 'warden' => OpenStruct.new(:message => :invalid))
-      assert_match '<error>Invalid email or password.</error>', @response.third.body
-    end
-
     test 'works for any non navigational format' do
       swap Devise, :navigational_formats => [] do
         call_failure('formats' => :html)
         assert_equal 401, @response.first
       end
     end
+
+    test 'uses the failure message as response body' do
+      call_failure('formats' => :xml, 'warden' => OpenStruct.new(:message => :invalid))
+      assert_match '<error>Invalid email or password.</error>', @response.third.body
+    end
+
+    context 'on ajax call' do
+      context 'when http_authenticatable_on_xhr is false' do
+        test 'dont return 401 with navigational formats' do
+          swap Devise, :http_authenticatable_on_xhr => false do
+            call_failure('formats' => :html, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
+            assert_equal 302, @response.first
+            assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
+          end
+        end
+
+        test 'dont return 401 with non navigational formats' do
+          swap Devise, :http_authenticatable_on_xhr => false do
+            call_failure('formats' => :json, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
+            assert_equal 302, @response.first
+            assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
+          end
+        end
+      end
+
+      context 'when http_authenticatable_on_xhr is true' do
+        test 'return 401' do
+          swap Devise, :http_authenticatable_on_xhr => true do
+            call_failure('formats' => :html, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
+            assert_equal 401, @response.first
+          end
+        end
+
+        test 'skip WWW-Authenticate header' do
+          swap Devise, :http_authenticatable_on_xhr => true do
+            call_failure('formats' => :html, 'HTTP_X_REQUESTED_WITH' => 'XMLHttpRequest')
+            assert_nil @response.second['WWW-Authenticate']
+          end
+        end
+      end
+    end
   end
 
   context 'With recall' do