diff --git a/activesupport/lib/active_support/option_merger.rb b/activesupport/lib/active_support/option_merger.rb
index 63662b75c7..e55ffd12c3 100644
--- a/activesupport/lib/active_support/option_merger.rb
+++ b/activesupport/lib/active_support/option_merger.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/hash/deep_merge'
+
 module ActiveSupport
   class OptionMerger #:nodoc:
     instance_methods.each do |method|