diff --git a/lib/doorkeeper.rb b/lib/doorkeeper.rb
index 31a363732..3432a7a53 100644
--- a/lib/doorkeeper.rb
+++ b/lib/doorkeeper.rb
@@ -29,6 +29,7 @@
 require "doorkeeper/oauth/token_request"
 require "doorkeeper/oauth/client"
 require "doorkeeper/oauth/token"
+require "doorkeeper/oauth/invalid_token_response"
 
 require 'doorkeeper/models/scopes'
 require 'doorkeeper/models/expirable'