diff --git a/mocha.css b/mocha.css
index 4cd9855cad..9e1b55b4be 100644
--- a/mocha.css
+++ b/mocha.css
@@ -135,6 +135,7 @@ body {
 #mocha .test pre.error {
   color: #c00;
   max-height: 300px;
+  overflow: auto;
 }
 
 #mocha .test pre {