Index: form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.265
diff -u -r1.265 form.inc
--- form.inc	4 Feb 2008 10:23:32 -0000	1.265
+++ form.inc	4 Feb 2008 17:27:19 -0000
@@ -664,10 +664,11 @@
   // Validate the current input.
   if (!isset($elements['#validated']) || !$elements['#validated']) {
     if (isset($elements['#needs_validation'])) {
-      // We only check for trimmed string length being zero. 0 might be
-      // a possible value with some field types, such as radio buttons, so
-      // empty() is not usable here.
-      if ($elements['#required'] && strlen(trim($elements['#value'])) == 0) {
+      // Some field types, such as radio buttons, are able to have return values
+      // of zero.  So we only check if the field is empty when a string is
+      // returned.
+      $is_empty = is_string($elements['#value']) ? empty($elements['#value']) : FALSE;
+      if ($elements['#required'] && $is_empty) == 0) {
         form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
       }