diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 15a3717ea193..59ffd2469818 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -6,6 +6,8 @@
 
 module ActiveSupport
   class HashWithIndifferentAccess < Hash
+    
+    # Always returns true, so that <tt>Array#extract_options!</tt> finds members of this class.
     def extractable_options?
       true
     end