diff --git a/src/Entity/Facet.php b/src/Entity/Facet.php
index 250c8e8..d387202 100644
--- a/src/Entity/Facet.php
+++ b/src/Entity/Facet.php
@@ -367,7 +367,7 @@ class Facet extends ConfigEntityBase implements FacetInterface {
    * {@inheritdoc}
    */
   public function getQueryOperator() {
-    return $this->query_operator ?: 'OR';
+    return $this->query_operator ?: 'or';
   }
 
   /**