diff --git a/root-cert-stats/background.js b/root-cert-stats/background.js
index 272fedad..59c70f34 100644
--- a/root-cert-stats/background.js
+++ b/root-cert-stats/background.js
@@ -1,6 +1,6 @@
 "use strict";
 
-let rootCertStats = {};
+var rootCertStats = {};
 
 /*
 On an onHeadersReceived event, if there was a successful TLS connection