diff --git a/lib/middleware.js b/lib/middleware.js
index 5473a15..011bd11 100644
--- a/lib/middleware.js
+++ b/lib/middleware.js
@@ -18,7 +18,7 @@ module.exports.create = function (le) {
 
   log(le.debug, "created middleware");
   return function () {
-    var prefix = le.acmeChallengePrefix; // /.well-known/acme-challenge/:token
+    var prefix = le.acmeChallengePrefix || '/.well-known/acme-challenge/';
 
     return function (req, res, next) {
       if (0 !== req.url.indexOf(prefix)) {