diff --git a/README.md b/README.md
index 3e375e4..f43425f 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@
 | [letsencrypt](https://github.com/Daplie/node-letsencrypt) (library)
 | [letsencrypt-cli](https://github.com/Daplie/letsencrypt-cli)
 | [letsencrypt-express](https://github.com/Daplie/letsencrypt-express)
+| [letsencrypt-cluster](https://github.com/Daplie/letsencrypt-cluster)
 | [letsencrypt-koa](https://github.com/Daplie/letsencrypt-koa)
 | [letsencrypt-hapi](https://github.com/Daplie/letsencrypt-hapi)
 |
@@ -57,3 +58,4 @@ For ACME Challenge:
 For node-letsencrypt internals:
 
 * `getOptions()` returns the internal defaults merged with the user-supplied options
+* `loopback(defaults, domain, key, value, done)` test, by external means, that the ACME server's challenge server will succeed
diff --git a/index.js b/index.js
index b121c37..3c8086c 100644
--- a/index.js
+++ b/index.js
@@ -40,6 +40,7 @@ Challenge.create = function (options) {
 //
 Challenge.set = function (args, domain, challengePath, keyAuthorization, done) {
   var mkdirp = require('mkdirp');
+  keyAuthorization = String(keyAuthorization);
 
   mkdirp(args.webrootPath, function (err) {
     if (err) {