diff --git a/src/Model/TemplateEngine/Decorator/InspectorHints.php b/src/Model/TemplateEngine/Decorator/InspectorHints.php
index 002d408..138768c 100644
--- a/src/Model/TemplateEngine/Decorator/InspectorHints.php
+++ b/src/Model/TemplateEngine/Decorator/InspectorHints.php
@@ -124,7 +124,7 @@ public function render(BlockInterface $block, $templateFile, array $dictionary =
     {
         // Measure render time
         $startTime = hrtime(true);
-        $result = $this->subject->render($block, $templateFile, $dictionary);
+        $result = (string) $this->subject->render($block, $templateFile, $dictionary);
         $endTime = hrtime(true);
 
         if (!$this->showBlockHints) {