diff --git a/uuid.entity.inc b/uuid.entity.inc
index 4fa037f..463dc6e 100644
--- a/uuid.entity.inc
+++ b/uuid.entity.inc
@@ -468,6 +468,11 @@ function entity_get_uuid_by_id($entity_type, $ids, $revision = FALSE) {
   else {
     return array();
   }
+  // Some contrib entities has no support for UUID, let's skip them.
+  // This means reference will be lost during conversion.
+  if ($uuid_key == NULL) {
+    return array();
+  }
 
   // Get all UUIDs in one query.
   return db_select($table, 't')