--- a/advagg_mod/src/Asset/DeferCss.php
+++ b/advagg_mod/src/Asset/DeferCss.php
@@ -67,6 +67,8 @@
       $path = drupal_get_path('module', 'advagg_mod') . '/js/loadCSS.js';
       if (!strpos($content, $path)) {
         $path = Crypt::hashBase64($path . $this->counter);
+      } else {
+        $path = str_replace('/', '\/', $path);
       }
       $pattern = "/<script src=['\"]\/(.*{$path}.*)\?.*['\"]>/";
       $content = preg_replace_callback($pattern, [$this, 'inlineScript'], $content);