diff --git a/lib/launcher.js b/lib/launcher.js
index f4815c0ac..67d1e204b 100644
--- a/lib/launcher.js
+++ b/lib/launcher.js
@@ -37,7 +37,7 @@ var Browser = function(id) {
     return [url];
   };
 
-  this._tempDir = (env.TMPDIR || env.TMP || env.TEMP || '/tmp') + '/testacular-' + id;
+  this._tempDir = (env.TMPDIR || env.TMP || env.TEMP || '/tmp') + '/testacular-' + id.toString();
 
   try {
     log.debug('Creating temp dir at ' + this._tempDir);