diff --git a/lib/main.js b/lib/main.js
index 2a7b5676..ad34deb0 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -250,7 +250,7 @@ Lambda.prototype._nativeZip = function (program, codeDirectory, callback) {
 Lambda.prototype._codeDirectory = function (program) {
   var epoch_time = +new Date();
 
-  return os.tmpDir() + '/' + program.functionName + '-' + epoch_time;
+  return path.join(os.tmpDir(), program.functionName + '-' + epoch_time);
 };
 
 Lambda.prototype._cleanDirectory = function (codeDirectory, callback) {