diff --git a/lib/webhookr/engine.rb b/lib/webhookr/engine.rb
index <HASH>..<HASH> 100644
--- a/lib/webhookr/engine.rb
+++ b/lib/webhookr/engine.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/kernel/singleton_class'
+
 module Webhookr
   class Engine < ::Rails::Engine
     isolate_namespace Webhookr
Added include for compat with Ruby <I>