diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index cd76383931..b5d62ad14e 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -681,7 +681,10 @@ module ActionMailer #:nodoc:
       end
     end
 
-    def default_i18n_subject #:nodoc:
+    # Translates the +subject+ using Rails I18n class under <tt>[:actionmailer, mailer_scope, action_name]</tt> scope.
+    # If it does not find a translation for the +subject+ under the specified scope it will default to a
+    # humanized version of the <tt>action_name</tt>.
+    def default_i18n_subject
       mailer_scope = self.class.mailer_name.gsub('/', '.')
       I18n.t(:subject, :scope => [mailer_scope, action_name], :default => action_name.humanize)
     end