diff --git a/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb b/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
index eaefdc0f15c4e5fe6e9c4caf9f0ea16586c2808c..af06bffa1632be1363a3bf750e9182166ea85119 100644
--- a/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
+++ b/actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
@@ -1,4 +1,5 @@
 require 'set'
+require 'cgi'
 require 'active_support/core_ext/class/attribute'
 
 module HTML