diff --git a/koa-router/koa-router-tests.ts b/koa-router/koa-router-tests.ts
index deaa7e083d..36d3e6c1c8 100644
--- a/koa-router/koa-router-tests.ts
+++ b/koa-router/koa-router-tests.ts
@@ -11,6 +11,9 @@ const router = new Router({
 });
 
 router
+  .param('id', function(id, ctx, next) {
+    next();
+  })
   .get('/', function (ctx, next) {
     ctx.body = 'Hello World!';
   })
@@ -23,7 +26,7 @@ router
   .del('/users/:id', function (ctx, next) {
     // ...
   });
-  
+
 router.get('user', '/users/:id', function (ctx, next) {
     ctx.body = "sdsd";
 });
diff --git a/koa-router/koa-router.d.ts b/koa-router/koa-router.d.ts
index d289657c84..25ec962dad 100644
--- a/koa-router/koa-router.d.ts
+++ b/koa-router/koa-router.d.ts
@@ -30,7 +30,7 @@ declare module "koa-router" {
 
         export interface IRouterOptions {
             /**
-             * Router prefixes 
+             * Router prefixes
              */
             prefix?: string;
             /**
@@ -52,6 +52,10 @@ declare module "koa-router" {
             (ctx: Router.IRouterContext, next?: () => any): any;
         }
 
+        export interface IParamMiddleware {
+            (param: string, ctx: Router.IRouterContext, next?: () => any): any;
+        }
+
         export interface IRouterAllowedMethodsOptions {
             /**
              * throw error instead of setting status and header
@@ -141,13 +145,13 @@ declare module "koa-router" {
          */
         get(name: string, path: string, ...middleware: Array<Router.IMiddleware>): Router;
         get(path: string, ...middleware: Array<Router.IMiddleware>): Router;
-        
+
         /**
          * HTTP post method
          */
         post(name: string, path: string, ...middleware: Array<Router.IMiddleware>): Router;
         post(path: string, ...middleware: Array<Router.IMiddleware>): Router;
-        
+
         /**
          * HTTP put method
          */
@@ -214,7 +218,7 @@ declare module "koa-router" {
 
         /**
          * Redirect `source` to `destination` URL with optional 30x status `code`.
-         * 
+         *
          * Both `source` and `destination` can be route names.
          */
         redirect(source: string, destination: string, code?: number): Router;
@@ -245,7 +249,7 @@ declare module "koa-router" {
         /**
          * Run middleware for named route parameters. Useful for auto-loading or validation.
          */
-        param(param: string, middleware: Router.IMiddleware): Router;
+        param(param: string, middleware: Router.IParamMiddleware): Router;
 
         /**
          * Generate URL from url pattern and given `params`.