diff --git a/config/locales/en.yml b/config/locales/en.yml
index e70ad899..258316ca 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -12,6 +12,7 @@ en:
 
   devise:
     failure:
+      no_authentication_allowed: 'You are attempting to access a resource as an authenticated user when that is not allowed. Please sign out and try again.'
       unauthenticated: 'You need to sign in or sign up before continuing.'
       unconfirmed: 'You have to confirm your account before continuing.'
       locked: 'Your account is locked.'
diff --git a/lib/devise/controllers/internal_helpers.rb b/lib/devise/controllers/internal_helpers.rb
index 3195f492..ce078936 100644
--- a/lib/devise/controllers/internal_helpers.rb
+++ b/lib/devise/controllers/internal_helpers.rb
@@ -114,6 +114,7 @@ MESSAGE
       def require_no_authentication
         if warden.authenticated?(resource_name)
           resource = warden.user(resource_name)
+          flash[:alert] = I18n.t("devise.failure.no_authentication_allowed")
           redirect_to after_sign_in_path_for(resource)
         end
       end
diff --git a/test/controllers/internal_helpers_test.rb b/test/controllers/internal_helpers_test.rb
index 518b887f..a44269d8 100644
--- a/test/controllers/internal_helpers_test.rb
+++ b/test/controllers/internal_helpers_test.rb
@@ -45,6 +45,14 @@ class HelpersTest < ActionController::TestCase
     @controller.send :require_no_authentication
   end
 
+  test 'require no authentication sets a flash message' do
+    @mock_warden.expects(:authenticated?).with(:user).returns(true)
+    @mock_warden.expects(:user).with(:user).returns(User.new)
+    @controller.expects(:redirect_to).with(root_path)
+    @controller.send :require_no_authentication
+    assert flash[:alert] == I18n.t("devise.failure.no_authentication_allowed")
+  end
+
   test 'signed in resource returns signed in resource for current scope' do
     @mock_warden.expects(:authenticate).with(:scope => :user).returns(User.new)
     assert_kind_of User, @controller.signed_in_resource