diff --git a/select_or_other.field_widget.inc b/select_or_other.field_widget.inc
index a16813d..1065f2d 100644
--- a/select_or_other.field_widget.inc
+++ b/select_or_other.field_widget.inc
@@ -138,6 +138,13 @@ function select_or_other_field_widget_form_prepare_options($field, $instance, $h
     natcasesort($options);
   }
 
+  // Align with Drupal core select list, NULL (-None-) value.
+  // http://drupal.org/node/1830090
+  if (isset($options['']['- None -']) || isset($options['']['- Select a value -'])) {
+    $value = $options[''];
+    unset($options['']);
+    $options['_none'] = $value;
+  }
   return $options;
 }