diff --git a/core/includes/form.inc b/core/includes/form.inc
index c94bc62..d9c87cb 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -3041,9 +3041,7 @@ function form_process_radios($element) {
         // The key is sanitized in drupal_attributes() during output from the
         // theme function.
         '#return_value' => $key,
-        // Use default or FALSE. A value of FALSE means that the radio button is
-        // not 'checked'.
-        '#default_value' => isset($element['#default_value']) ? $element['#default_value'] : FALSE,
+        '#default_value' => isset($element['#default_value']) ? $element['#default_value'] : NULL,
         '#attributes' => $element['#attributes'],
         '#parents' => $element['#parents'],
         '#id' => drupal_html_id('edit-' . implode('-', $parents_for_id)),