diff --git a/index.js b/index.js
index eb42310..27e736f 100644
--- a/index.js
+++ b/index.js
@@ -7,7 +7,7 @@ module.exports = accesslog;
 function accesslog(req, res, format, cb) {
   if (typeof format === 'function') {
     cb = format;
-    format = null;
+    format = undefined;
   }
 
   var remoteAddress = req.connection.remoteAddress;
diff --git a/package.json b/package.json
index f873736..a0608a6 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "access-log",
   "description": "Add simple access logs to any http or https server",
-  "version": "0.4.1",
+  "version": "0.4.2",
   "author": "Dave Eddy <dave@daveeddy.com> (http://www.daveeddy.com)",
   "contributors": [],
   "repository": {