diff --git a/lib/internal/Magento/Framework/View/Page/Config.php b/lib/internal/Magento/Framework/View/Page/Config.php
index aafb5eda9b617..529f8b02e0635 100644
--- a/lib/internal/Magento/Framework/View/Page/Config.php
+++ b/lib/internal/Magento/Framework/View/Page/Config.php
@@ -174,7 +174,7 @@ public function __construct(
         $this->setElementAttribute(
             self::ELEMENT_TYPE_HTML,
             self::HTML_ATTRIBUTE_LANG,
-            str_replace('_', '-', $this->localeResolver->getLocale())
+            strstr($this->localeResolver->getLocale(), '_', true)
         );
     }