diff --git a/boot.js b/boot.js
index 201a94a..9aa0bc0 100644
--- a/boot.js
+++ b/boot.js
@@ -6,7 +6,6 @@ const inherits = require('util').inherits
 const {
   AVV_ERR_EXPOSE_ALREADY_DEFINED,
   AVV_ERR_CALLBACK_NOT_FN,
-  AVV_ERR_PLUGIN_NOT_VALID,
   AVV_ERR_ROOT_PLG_BOOTED,
   AVV_ERR_READY_TIMEOUT
 } = require('./lib/errors')
@@ -18,6 +17,8 @@ const {
 const { TimeTree } = require('./lib/time-tree')
 const { Plugin } = require('./plugin')
 const { debug } = require('./lib/debug')
+const { validatePlugin } = require('./lib/validate-plugin')
+const { isBundledOrTypescriptPlugin } = require('./lib/is-bundled-or-typescript-plugin')
 const { loadPlugin } = require('./lib/load-plugin')
 
 function wrap (server, opts, instance) {
@@ -201,18 +202,6 @@ Boot.prototype.override = function (server, func, opts) {
   return server
 }
 
-function assertPlugin (plugin) {
-  // Faux modules are modules built with TypeScript
-  // or Babel that they export a .default property.
-  if (plugin && typeof plugin === 'object' && typeof plugin.default === 'function') {
-    plugin = plugin.default
-  }
-  if (!(plugin && (typeof plugin === 'function' || typeof plugin.then === 'function'))) {
-    throw new AVV_ERR_PLUGIN_NOT_VALID(typeof plugin)
-  }
-  return plugin
-}
-
 Boot.prototype[kAvvio] = true
 
 // load a plugin
@@ -241,7 +230,10 @@ Boot.prototype._loadRegistered = function () {
 Object.defineProperty(Boot.prototype, 'then', { get: thenify })
 
 Boot.prototype._addPlugin = function (plugin, opts, isAfter) {
-  plugin = assertPlugin(plugin)
+  if (isBundledOrTypescriptPlugin(plugin)) {
+    plugin = plugin.default
+  }
+  validatePlugin(plugin)
   opts = opts || {}
 
   if (this.booted) {
diff --git a/lib/is-bundled-or-typescript-plugin.js b/lib/is-bundled-or-typescript-plugin.js
new file mode 100644
index 0000000..f72438e
--- /dev/null
+++ b/lib/is-bundled-or-typescript-plugin.js
@@ -0,0 +1,20 @@
+'use strict'
+
+/**
+ * bundled or typescript plugin
+ * @typedef {object} BundledOrTypescriptPlugin
+ * @property {function} default
+ */
+
+/**
+ * @param {unknown} plugin
+ * @returns {plugin is BundledOrTypescriptPlugin}
+ */
+
+function isBundledOrTypescriptPlugin (plugin) {
+  return plugin !== null && typeof plugin === 'object' && typeof plugin.default === 'function'
+}
+
+module.exports = {
+  isBundledOrTypescriptPlugin
+}
diff --git a/lib/validate-plugin.js b/lib/validate-plugin.js
new file mode 100644
index 0000000..4006ca4
--- /dev/null
+++ b/lib/validate-plugin.js
@@ -0,0 +1,25 @@
+'use strict'
+
+const { AVV_ERR_PLUGIN_NOT_VALID } = require('./errors')
+
+/**
+ * @param {unknown} plugin
+ * @throws {AVV_ERR_PLUGIN_NOT_VALID}
+ * @returns {Function}
+ */
+function validatePlugin (plugin) {
+  // validate if plugin is a function or Promise
+  if (!(plugin && (typeof plugin === 'function' || typeof plugin.then === 'function'))) {
+    if (Array.isArray(plugin)) {
+      throw new AVV_ERR_PLUGIN_NOT_VALID('array')
+    } else if (plugin === null) {
+      throw new AVV_ERR_PLUGIN_NOT_VALID('null')
+    } else {
+      throw new AVV_ERR_PLUGIN_NOT_VALID(typeof plugin)
+    }
+  }
+}
+
+module.exports = {
+  validatePlugin
+}
diff --git a/test/lib/is-bundled-or-typescript-plugin.test.js b/test/lib/is-bundled-or-typescript-plugin.test.js
new file mode 100644
index 0000000..b81029b
--- /dev/null
+++ b/test/lib/is-bundled-or-typescript-plugin.test.js
@@ -0,0 +1,20 @@
+'use strict'
+
+const { test } = require('tap')
+const { isBundledOrTypescriptPlugin } = require('../../lib/is-bundled-or-typescript-plugin')
+
+test('isBundledOrTypescriptPlugin', (t) => {
+  t.plan(9)
+
+  t.equal(isBundledOrTypescriptPlugin(1), false)
+  t.equal(isBundledOrTypescriptPlugin('function'), false)
+  t.equal(isBundledOrTypescriptPlugin({}), false)
+  t.equal(isBundledOrTypescriptPlugin([]), false)
+  t.equal(isBundledOrTypescriptPlugin(null), false)
+
+  t.equal(isBundledOrTypescriptPlugin(function () {}), false)
+  t.equal(isBundledOrTypescriptPlugin(new Promise((resolve) => resolve)), false)
+  t.equal(isBundledOrTypescriptPlugin(Promise.resolve()), false)
+
+  t.equal(isBundledOrTypescriptPlugin({ default: () => {} }), true)
+})
diff --git a/test/lib/validate-plugin.test.js b/test/lib/validate-plugin.test.js
new file mode 100644
index 0000000..a3aa956
--- /dev/null
+++ b/test/lib/validate-plugin.test.js
@@ -0,0 +1,19 @@
+'use strict'
+
+const { test } = require('tap')
+const { validatePlugin } = require('../../lib/validate-plugin')
+const { AVV_ERR_PLUGIN_NOT_VALID } = require('../../lib/errors')
+
+test('validatePlugin', (t) => {
+  t.plan(8)
+
+  t.throws(() => validatePlugin(1), new AVV_ERR_PLUGIN_NOT_VALID('number'))
+  t.throws(() => validatePlugin('function'), new AVV_ERR_PLUGIN_NOT_VALID('string'))
+  t.throws(() => validatePlugin({}), new AVV_ERR_PLUGIN_NOT_VALID('object'))
+  t.throws(() => validatePlugin([]), new AVV_ERR_PLUGIN_NOT_VALID('array'))
+  t.throws(() => validatePlugin(null), new AVV_ERR_PLUGIN_NOT_VALID('null'))
+
+  t.doesNotThrow(() => validatePlugin(function () {}))
+  t.doesNotThrow(() => validatePlugin(new Promise((resolve) => resolve)))
+  t.doesNotThrow(() => validatePlugin(Promise.resolve()))
+})