diff --git a/lib/active_admin/sortable_tree.rb b/lib/active_admin/sortable_tree.rb
index 7174a3c..9ebc327 100644
--- a/lib/active_admin/sortable_tree.rb
+++ b/lib/active_admin/sortable_tree.rb
@@ -1,3 +1,5 @@
+require 'activeadmin'
+
 require 'active_admin/sortable_tree/compatibility'
 require 'active_admin/sortable_tree/engine'
 require 'active_admin/sortable_tree/controller_actions'