diff --git a/www/vendor/magento/module-customer/Model/Indexer/Source.php b/www/vendor/magento/module-customer/Model/Indexer/Source.php
index e4bf03e08..c04a37b47 100644
--- a/www/vendor/magento/module-customer/Model/Indexer/Source.php
+++ b/www/vendor/magento/module-customer/Model/Indexer/Source.php
@@ -69,6 +69,17 @@ class Source implements \IteratorAggregate, \Countable, SourceProviderInterface
         return $this->customerCollection->getSelect();
     }
 
+    // REF-PATCH START added missing function addAttributeToSelect
+    /**
+     * {@inheritdoc}
+     */
+    public function addAttributeToSelect($fieldName, $alias = null)
+    {
+        $this->customerCollection->addAttributeToSelect($fieldName, $alias);
+        return $this;
+    }
+    //REF-PATCH END
+
     /**
      * {@inheritdoc}
      */