diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index d8b08116eb..24be66d197 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -599,6 +599,7 @@ module ActionMailer #:nodoc:
       end
 
       def render(opts)
+        opts[:locals] ||= {}
         layout, file = opts.delete(:layout), opts[:file]
 
         begin