diff --git a/includes/form.inc b/includes/form.inc
index e749239ef..c265e5466 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -1387,7 +1387,10 @@ function _form_validate(&$elements, &$form_state, $form_id = NULL) {
         // identical to the empty option's value, we reset the element's value
         // to NULL to trigger the regular #required handling below.
         // @see form_process_select()
-        elseif ($elements['#type'] == 'select' && !$elements['#multiple'] && $elements['#required'] && !isset($elements['#default_value']) && $elements['#value'] === $elements['#empty_value']) {
+        elseif ($elements['#type'] == 'select' && $elements['#required']
+        && (!array_key_exists('#multiple', $elements) || !$elements['#multiple'])
+        && !isset($elements['#default_value'])
+        && $elements['#value'] === $elements['#empty_value']) {
           $elements['#value'] = NULL;
           form_set_value($elements, NULL, $form_state);
         }