diff --git a/lib/devise/delegator.rb b/lib/devise/delegator.rb
index 1e7c8b79..361d4cff 100644
--- a/lib/devise/delegator.rb
+++ b/lib/devise/delegator.rb
@@ -8,9 +8,9 @@ module Devise
     def failure_app(env)
       app = env["warden.options"] &&
         (scope = env["warden.options"][:scope]) &&
-        Devise.mappings[scope].failure_app
+        Devise.mappings[scope.to_sym].failure_app
 
       app || Devise::FailureApp
     end
   end
-end
\ No newline at end of file
+end
diff --git a/test/delegator_test.rb b/test/delegator_test.rb
new file mode 100644
index 00000000..1618be10
--- /dev/null
+++ b/test/delegator_test.rb
@@ -0,0 +1,19 @@
+require 'test_helper'
+
+class DelegatorTest < ActiveSupport::TestCase
+  def delegator
+    Devise::Delegator.new
+  end
+
+  test 'failure_app returns default failure app if no warden options in env' do
+    assert_equal Devise::FailureApp, delegator.failure_app({})
+  end
+
+  test 'failure_app returns default failure app if no scope in warden options' do
+    assert_equal Devise::FailureApp, delegator.failure_app({"warden.options" => {}})
+  end
+
+  test 'failure_app returns associated failure app by scope in the given environment' do
+    assert_kind_of Proc, delegator.failure_app({"warden.options" => {:scope => "manager"}})
+  end
+end