diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index e1a480c2fb..3c41691af7 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -3,6 +3,7 @@ require 'action_mailer/tmail_compat'
 require 'action_mailer/collector'
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/proc'
 
 module ActionMailer #:nodoc:
   # Action Mailer allows you to send email from your application using a mailer model and views.