diff --git a/system/src/Grav/Common/Grav.php b/system/src/Grav/Common/Grav.php
index c2ccfcb5a..1c639e830 100644
--- a/system/src/Grav/Common/Grav.php
+++ b/system/src/Grav/Common/Grav.php
@@ -235,7 +235,7 @@ class Grav extends Container
 
         // Calculate a Hash based on the raw file
         if ($page->eTag()) {
-            header('ETag: ' . md5($page->raw() . $page->modified()));
+            header('ETag: "' . md5($page->raw() . $page->modified()).'"');
         }
 
         // Set debugger data in headers