diff --git a/gulp/util/bundle.js b/gulp/util/bundle.js
index 7eecd98..b076faa 100644
--- a/gulp/util/bundle.js
+++ b/gulp/util/bundle.js
@@ -33,9 +33,11 @@
 function watch(onUpdate) {
     var bundler = watchify(createBundler(watchify.args));
 
-    bundler.on('update', function () {
-        rebundle.call(this).on('end', onUpdate);
-    });
+    if (onUpdate) {
+        bundler.on('update', function () {
+            rebundle.call(this).on('end', onUpdate);
+        });
+    }
 
     return rebundle.call(bundler);
 }