diff --git a/core/includes/form.inc b/core/includes/form.inc
index 8440609..4d87abc 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -2766,7 +2766,7 @@ function theme_radio($variables) {
   $element['#attributes']['type'] = 'radio';
   element_set_attributes($element, array('id', 'name', '#return_value' => 'value'));
 
-  if (isset($element['#return_value']) && $element['#value'] == $element['#return_value']) {
+  if (isset($element['#return_value']) && $element['#value'] !== FALSE && $element['#value'] == $element['#return_value']) {
     $element['#attributes']['checked'] = 'checked';
   }
   _form_set_class($element, array('form-radio'));
@@ -2998,7 +2998,9 @@ function form_process_radios($element) {
         // The key is sanitized in drupal_attributes() during output from the
         // theme function.
         '#return_value' => $key,
-        '#default_value' => isset($element['#default_value']) ? $element['#default_value'] : NULL,
+        // Use default or FALSE. A value of FALSE means that the radio button is
+        // not 'checked'.
+        '#default_value' => isset($element['#default_value']) ? $element['#default_value'] : FALSE,
         '#attributes' => $element['#attributes'],
         '#parents' => $element['#parents'],
         '#id' => drupal_html_id('edit-' . implode('-', $parents_for_id)),