diff --git a/lib/application.js b/lib/application.js
index 1b1766d..866a1b8 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -113,7 +113,7 @@ app.use = function(fn){
 app.callback = function(){
   var mw = [respond].concat(this.middleware);
   var gen = compose(mw);
-  var fn = co(gen);
+  var fn = co.wrap(gen);
   var self = this;
 
   if (!this.listeners('error').length) this.on('error', this.onerror);
@@ -122,7 +122,7 @@ app.callback = function(){
     res.statusCode = 404;
     var ctx = self.createContext(req, res);
     onFinished(res, ctx.onerror);
-    fn.call(ctx, ctx.onerror);
+    fn.call(ctx).catch(ctx.onerror);
   }
 };
 
diff --git a/package.json b/package.json
index 5466584..c0f2a37 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,7 @@
   "license": "MIT",
   "dependencies": {
     "accepts": "^1.1.0",
-    "co": "^3.1.0",
+    "co": "^4.0.0",
     "content-disposition": "~0.5.0",
     "cookies": "~0.5.0",
     "debug": "*",