diff --git a/src/Whoops/Resources/js/whoops.base.js b/src/Whoops/Resources/js/whoops.base.js
index 5c0cdab6..20730b02 100644
--- a/src/Whoops/Resources/js/whoops.base.js
+++ b/src/Whoops/Resources/js/whoops.base.js
@@ -100,7 +100,7 @@ Zepto(function($) {
 
   var clipboard = new Clipboard('.clipboard');
   var showTooltip = function(elem, msg) {
-    elem.setAttribute('class', 'clipboard tooltipped tooltipped-s');
+    elem.classList.add('tooltipped', 'tooltipped-s');
     elem.setAttribute('aria-label', msg);
   };
 
@@ -117,7 +117,7 @@ Zepto(function($) {
   var btn = document.querySelector('.clipboard');
 
   btn.addEventListener('mouseleave', function(e) {
-    e.currentTarget.setAttribute('class', 'rightButton clipboard');
+    e.currentTarget.classList.remove('tooltipped', 'tooltipped-s');
     e.currentTarget.removeAttribute('aria-label');
   });