diff --git a/package.json b/package.json
index 23efae7..2f3a439 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "koa-oai-router",
-  "version": "2.0.0-alpha.1",
+  "version": "2.0.0-alpha.2",
   "main": "lib",
   "scripts": {
     "clean": "rm -rf coverage lib",
diff --git a/src/plugin.js b/src/plugin.js
index 1f9ac4c..49bee28 100644
--- a/src/plugin.js
+++ b/src/plugin.js
@@ -17,7 +17,6 @@ class Plugin {
     assert(_.isString(name), 'name must be string.');
     assert(_.isString(field) || (_.isArray(field) && _.every(field, _.isString)), 'field must be string or [string].');
     assert(_.isFunction(middlewareWrapper), 'middlewareWrapper must be function.');
-    assert(_.isObject(middlewareArgs) || _.isUndefined(middlewareArgs), 'middlewareWrapper must be object.');
 
     this.name = name;
     this.field = field;