diff --git a/entityreference.module b/entityreference.module
index bdcb562..297a9f2 100644
--- a/entityreference.module
+++ b/entityreference.module
@@ -975,11 +975,11 @@ function entityreference_autocomplete_access_callback($type, $field_name, $entit
  *   The bundle name.
  * @param $entity_id
  *   Optional; The entity ID the entity-reference field is attached to.
- *   Defaults to ''.
+ *   Defaults to 'NULL'.
  * @param $string
  *   The label of the entity to query by.
  */
-function entityreference_autocomplete_callback($type, $field_name, $entity_type, $bundle_name, $entity_id = '', $string = '') {
+function entityreference_autocomplete_callback($type, $field_name, $entity_type, $bundle_name, $entity_id = 'NULL', $string = '') {
   // If the request has a '/' in the search text, then the menu system will have
   // split it into multiple arguments and $string will only be a partial. We want
   //  to make sure we recover the intended $string.