diff --git a/actionpack/lib/action_view/helpers/date_helper.rb b/actionpack/lib/action_view/helpers/date_helper.rb
index <HASH>..<HASH> 100644
--- a/actionpack/lib/action_view/helpers/date_helper.rb
+++ b/actionpack/lib/action_view/helpers/date_helper.rb
@@ -880,7 +880,7 @@ module ActionView
 
         def translated_date_order
           date_order = I18n.translate(:'date.order', :locale => @options[:locale], :default => [])
-          date_order.map! { |element| element.to_sym }
+          date_order = date_order.map { |element| element.to_sym }
 
           forbidden_elements = date_order - [:year, :month, :day]
           if forbidden_elements.any?
Don't change the original i<I>n data