diff --git a/lib/internal/Magento/Framework/View/Model/Layout/Merge.php b/lib/internal/Magento/Framework/View/Model/Layout/Merge.php
index ea8f74107954c..fe5c94ed21b30 100644
--- a/lib/internal/Magento/Framework/View/Model/Layout/Merge.php
+++ b/lib/internal/Magento/Framework/View/Model/Layout/Merge.php
@@ -811,7 +811,7 @@ private function getXmlErrors($libXmlErrors)
     protected function _getPhysicalTheme(\Magento\Framework\View\Design\ThemeInterface $theme)
     {
         $result = $theme;
-        while ($result->getId() && !$result->isPhysical()) {
+        while ($result !== null && $result->getId() && !$result->isPhysical()) {
             $result = $result->getParentTheme();
         }
         if (!$result) {