diff --git a/assets/js/main.js b/assets/js/main.js
index 9c92789..620db5d 100644
--- a/assets/js/main.js
+++ b/assets/js/main.js
@@ -21,7 +21,7 @@ jQuery(function($) {
 
     _Blog.toggleTheme = function() {
         const currentTheme = window.localStorage && window.localStorage.getItem('theme')
-        const isDark = currentTheme === undefined || currentTheme === 'dark'
+        const isDark = currentTheme === null || currentTheme === 'dark'
         $('body').toggleClass('dark-theme', isDark)
         $('.theme-switch').on('click', () => {
             $('body').toggleClass('dark-theme')