diff --git a/lib/application.js b/lib/application.js
index 0f41306..3bbb60c 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -37,11 +37,7 @@ function Application() {
   this.poweredBy = true;
   this.jsonSpaces = 2;
   this.middleware = [];
-  this._Context = function Context(app, req, res){
-    this.app = app;
-    this.req = req;
-    this.res = res;
-  }
+  this.Context = createContext(); 
   this.context(context);
 }
 
@@ -101,7 +97,7 @@ app.use = function(fn){
  */
 
 app.context = function(obj){
-  var ctx = this._Context.prototype;
+  var ctx = this.Context.prototype;
   Object.getOwnPropertyNames(obj).forEach(function(name){
     var descriptor = Object.getOwnPropertyDescriptor(obj, name);
     Object.defineProperty(ctx, name, descriptor);
@@ -123,7 +119,7 @@ app.callback = function(){
   var self = this;
 
   return function(req, res){
-    var ctx = new self._Context(self, req, res);
+    var ctx = new self.Context(self, req, res);
 
     function done(err) {
       if (err) ctx.error(err);
@@ -198,9 +194,26 @@ function respond(next){
 
 /**
  * Default downstream middleware.
+ *
+ * @api private
  */
 
 function *downstream() {
   this.status = 200;
   if (this.app.poweredBy) this.set('X-Powered-By', 'koa');
 }
+
+/**
+ * Create a new `Context` constructor.
+ *
+ * @return {Function}
+ * @api private
+ */
+
+function createContext() {
+  return function Context(app, req, res){
+    this.app = app;
+    this.req = req;
+    this.res = res;
+  }
+}