diff --git a/extended-toc.php b/extended-toc.php
index 58d8709..eeada82 100644
--- a/extended-toc.php
+++ b/extended-toc.php
@@ -293,7 +293,7 @@ if( !class_exists('ExToC') ) {
     }
         
     public function wp_enqueue_scripts() {
-      wp_register_style(EXTENDED_TOC_ID, $this->path . '/style.css', array(), POWER_TOC_VERSION);
+      wp_register_style(EXTENDED_TOC_ID, $this->path . '/style.css', array(), 'POWER_TOC_VERSION');
       wp_enqueue_style(EXTENDED_TOC_ID);
     }