diff --git a/fivestar.module b/fivestar.module
index e40aa80..683dce6 100644
--- a/fivestar.module
+++ b/fivestar.module
@@ -1020,9 +1020,9 @@ function _fivestar_allow_vote($element) {
 /**
  * Implementation of hook_ctools_content_subtype_alter()
  */
-function fivestar_ctools_content_subtype_alter(&$subtype, &$plugin, $subtype_id) {
-  if ($plugin['name'] == 'entity_field') {
-    list($entity_type, $field_name) = explode(':', $subtype_id, 2);
+function fivestar_ctools_content_subtype_alter(&$subtype, &$plugin) {
+  if ($plugin['name'] == 'entity_field' && isset($subtype['subtype_id'])) {
+    list($entity_type, $field_name) = explode(':', $subtype['subtype_id'], 2);
     $field = field_info_field($field_name);
     if ($field['type'] == 'fivestar') {
       $subtype['render callback'] = 'fivestar_fivestar_field_content_type_render';