diff --git a/actionpack/lib/action_view/helpers/date_helper.rb b/actionpack/lib/action_view/helpers/date_helper.rb
index 9891478606a5e3ed9e8e20d8423c87a621deda2b..3aee4fb773a07fcd36092b7ffaaad655c9a73e1f 100644
--- a/actionpack/lib/action_view/helpers/date_helper.rb
+++ b/actionpack/lib/action_view/helpers/date_helper.rb
@@ -923,6 +923,7 @@ def to_datetime_select_tag(options = {}, html_options = {})
       private
         def datetime_selector(options, html_options)
           datetime = value(object) || default_datetime(options)
+          @auto_index ||= nil
 
           options = options.dup
           options[:field_name]           = @method_name