diff --git a/types/koa/index.d.ts b/types/koa/index.d.ts
index 07ddadc0c8..ea6bd60a46 100644
--- a/types/koa/index.d.ts
+++ b/types/koa/index.d.ts
@@ -659,8 +659,6 @@ declare namespace Application {
          * Default error handling.
          */
         onerror(err: Error): void;
-
-        [key: string]: any;
     }
 
     interface Request extends BaseRequest {
diff --git a/types/koa/koa-tests.ts b/types/koa/koa-tests.ts
index ea0a4a18b8..2ddf9b41e2 100644
--- a/types/koa/koa-tests.ts
+++ b/types/koa/koa-tests.ts
@@ -1,11 +1,21 @@
 import Koa = require("koa");
 
+declare module 'koa' {
+    export interface BaseContext {
+        db(): void;
+    }
+    export interface Context {
+        user: {};
+    }
+}
+
 const app = new Koa();
 
 app.context.db = () => {};
 
 app.use(async ctx => {
     console.log(ctx.db);
+    ctx.user = {};
 });
 
 app.use((ctx, next) => {