commit 6fc019c578f4900f8677cc184c1a4bb26d41df6f
Author: Joel Pittet <joel@pittet.ca>
Date:   Sat Feb 8 19:28:19 2014 -0800

    typo from core

diff --git a/core/includes/form.inc b/core/includes/form.inc
index bb6a140..32ab7a1 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -1138,7 +1138,7 @@ function password_confirm_validate($element, &$element_state) {
 function form_pre_render_date($element) {
   $element['#attributes']['type'] = 'date';
   element_set_attributes($element, array('id', 'name', 'type', 'min', 'max', 'step', 'value', 'size'));
-  _form_set_attributes($element, array('form-' . $element['attribute']['type']));
+  _form_set_attributes($element, array('form-' . $element['attributes']['type']));
 
   return $element;
 }