diff --git a/modules/taxonomy/taxonomy.module b/modules/taxonomy/taxonomy.module
index d7e9b2f..295120e 100644
--- a/modules/taxonomy/taxonomy.module
+++ b/modules/taxonomy/taxonomy.module
@@ -1372,7 +1372,7 @@ function taxonomy_field_widget_info_alter(&$info) {
 /**
  * Implements hook_options_list().
  */
-function taxonomy_options_list($field, $instance, $entity_type, $entity) {
+function taxonomy_options_list($field, $instance = NULL, $entity_type = NULL, $entity = NULL) {
   $function = !empty($field['settings']['options_list_callback']) ? $field['settings']['options_list_callback'] : 'taxonomy_allowed_values';
   return $function($field);
 }