diff --git a/tests/mocha/index.html b/tests/mocha/index.html
index c3e0272f0..604064c67 100644
--- a/tests/mocha/index.html
+++ b/tests/mocha/index.html
@@ -12,7 +12,7 @@
   <body>
 
     <div id="mocha"></div>
-    <div id="failureCount" style="display:none"></div>
+    <div id="failureCount" style="display:none" tests_failed="unset"></div>
     <script src="https://unpkg.com/chai/chai.js"></script>
     <script src="https://unpkg.com/mocha@5.2.0/mocha.js"></script>
     <script src="https://unpkg.com/sinon/pkg/sinon.js"></script>
