--- includes/form.inc.orig	2010-07-16 14:14:34.078125000 +0200
+++ includes/form.inc	2010-07-16 17:55:35.453125000 +0200
@@ -682,7 +682,9 @@ function _form_validate($elements, &$for
       // A simple call to empty() will not cut it here as some fields, like
       // checkboxes, can return a valid value of '0'. Instead, check the
       // length if it's a string, and the item count if it's an array.
-      if ($elements['#required'] && (!count($elements['#value']) || (is_string($elements['#value']) && strlen(trim($elements['#value'])) == 0))) {
+      // An unchecked checkbox has a #value of integer 0, different than string
+      // '0', which could be a valid value.
+      if ($elements['#required'] && (!count($elements['#value']) || (is_string($elements['#value']) && strlen(trim($elements['#value'])) == 0) || $elements['#value'] === 0)) {
         form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
       }
 
@@ -1877,6 +1879,7 @@ function theme_item($element) {
  * @ingroup themeable
  */
 function theme_checkbox($element) {
+  $t = get_t();
   _form_set_class($element, array('form-checkbox'));
   $checkbox = '<input ';
   $checkbox .= 'type="checkbox" ';
@@ -1887,7 +1890,9 @@ function theme_checkbox($element) {
   $checkbox .= drupal_attributes($element['#attributes']) .' />';
 
   if (!is_null($element['#title'])) {
-    $checkbox = '<label class="option" for="'. $element['#id'] .'">'. $checkbox .' '. $element['#title'] .'</label>';
+    $title = $element['#title'];
+    $required = !empty($element['#required']) ? '<span class="form-required" title="'. $t('This field is required.') .'">*</span>' : '';
+    $checkbox = '<label class="option" for="'. $element['#id'] .'">'. $checkbox .' '. $t('!title !required', array('!title' => filter_xss_admin($title), '!required' => $required)) .'</label>';
   }
 
   unset($element['#title']);