diff --git a/lib/active_admin.rb b/lib/active_admin.rb
index <HASH>..<HASH> 100644
--- a/lib/active_admin.rb
+++ b/lib/active_admin.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/class/attribute' # needed for Ransack
+require 'active_support/core_ext'
+require 'set'
+
 require 'ransack'
 require 'ransack_ext'
 require 'bourbon'
clearly require dependencies

activerecord-hackery/ransack#<I>