diff --git a/Twig/DataGridExtension.php b/Twig/DataGridExtension.php
index 77f37b1b..df4439f5 100644
--- a/Twig/DataGridExtension.php
+++ b/Twig/DataGridExtension.php
@@ -452,7 +452,7 @@ protected function getTemplatesFromString(Twig_Environment $environment, $theme)
         $this->templates = [];
 
         $template = $environment->loadTemplate($theme);
-        while ($template !== null) {
+        while ($template instanceof \Twig_Template) {
             $this->templates[] = $template;
             $template = $template->getParent([]);
         }