diff --git a/app/controllers/devise/two_factor_authentication_controller.rb b/app/controllers/devise/two_factor_authentication_controller.rb
index 1f2ac65..e302e01 100644
--- a/app/controllers/devise/two_factor_authentication_controller.rb
+++ b/app/controllers/devise/two_factor_authentication_controller.rb
@@ -9,7 +9,7 @@ class Devise::TwoFactorAuthenticationController < DeviseController
     render :show and return if params[:code].nil?
 
     if resource.authenticate_otp(params[:code])
-      warden.session(resource_name)[:need_two_factor_authentication] = false
+      warden.session(resource_name)[TwoFactorAuthentication::NEED_AUTHENTICATION] = false
       sign_in resource_name, resource, :bypass => true
       set_flash_message :notice, :success
       redirect_to stored_location_for(resource_name) || :root
diff --git a/lib/two_factor_authentication.rb b/lib/two_factor_authentication.rb
index 3e6e67e..0d985ac 100644
--- a/lib/two_factor_authentication.rb
+++ b/lib/two_factor_authentication.rb
@@ -16,6 +16,8 @@ module Devise
 end
 
 module TwoFactorAuthentication
+  NEED_AUTHENTICATION = 'need_two_factor_authentication'
+
   autoload :Schema, 'two_factor_authentication/schema'
   module Controllers
     autoload :Helpers, 'two_factor_authentication/controllers/helpers'
diff --git a/lib/two_factor_authentication/controllers/helpers.rb b/lib/two_factor_authentication/controllers/helpers.rb
index ef38330..5c151b2 100644
--- a/lib/two_factor_authentication/controllers/helpers.rb
+++ b/lib/two_factor_authentication/controllers/helpers.rb
@@ -12,7 +12,7 @@ module TwoFactorAuthentication
       def handle_two_factor_authentication
         unless devise_controller?
           Devise.mappings.keys.flatten.any? do |scope|
-            if signed_in?(scope) and warden.session(scope)[:need_two_factor_authentication]
+            if signed_in?(scope) and warden.session(scope)[TwoFactorAuthentication::NEED_AUTHENTICATION]
               handle_failed_second_factor(scope)
             end
           end
@@ -42,7 +42,9 @@ module Devise
   module Controllers
     module Helpers
       def is_fully_authenticated?
-        !session["warden.user.user.session"].try(:[], :need_two_factor_authentication)
+        !session["warden.user.user.session"].try(:[],
+          TwoFactorAuthentication::NEED_AUTHENTICATION
+        )
       end
     end
   end
diff --git a/lib/two_factor_authentication/hooks/two_factor_authenticatable.rb b/lib/two_factor_authentication/hooks/two_factor_authenticatable.rb
index 2abb4a4..985dc34 100644
--- a/lib/two_factor_authentication/hooks/two_factor_authenticatable.rb
+++ b/lib/two_factor_authentication/hooks/two_factor_authenticatable.rb
@@ -1,6 +1,6 @@
 Warden::Manager.after_authentication do |user, auth, options|
   if user.respond_to?(:need_two_factor_authentication?)
-    if auth.session(options[:scope])[:need_two_factor_authentication] = user.need_two_factor_authentication?(auth.request)
+    if auth.session(options[:scope])[TwoFactorAuthentication::NEED_AUTHENTICATION] = user.need_two_factor_authentication?(auth.request)
       user.send_two_factor_authentication_code
     end
   end