diff --git a/lib/application.js b/lib/application.js
index da7674e..9d2f11b 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -131,7 +131,7 @@ app.callback = function(){
 
     co.call(ctx, function *(){
       yield fn;
-    }, function(err){
+    })(function(err){
       if (err) ctx.onerror(err);
     });
   }
diff --git a/package.json b/package.json
index 24f5d1f..68194e6 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
   ],
   "license": "MIT",
   "dependencies": {
-    "co": "1.5.1",
+    "co": "2.0.0",
     "debug": "*",
     "mime": "1.2.10",
     "fresh": "0.2.0",