diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticsearchOptions.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticsearchOptions.php
index 22918b8b3a..d65221dc8f 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticsearchOptions.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticsearchOptions.php
@@ -38,7 +38,7 @@ class ElasticsearchOptions
     private $populateDirection;
 
     /** @var  int[] */
-    private $_customValues;
+    private $_customValues = [];
     private $activeTab;
 
     /**