diff --git a/decls/validator.js b/decls/validator.js
index <HASH>..<HASH> 100644
--- a/decls/validator.js
+++ b/decls/validator.js
@@ -3,6 +3,8 @@ declare type ValidatorDefinition = {
   message?: string|Function // error message
 }
 
+declare type ValidatorAsset = Function|ValidatorDefinition
+
 declare type ValidationError = {
   field: string,
   validator: string,
diff --git a/src/asset.js b/src/asset.js
index <HASH>..<HASH> 100644
--- a/src/asset.js
+++ b/src/asset.js
@@ -30,8 +30,8 @@ export default function (Vue: GlobalAPI): void {
    */
   function validator (
     id: string,
-    def?: Function | ValidatorDefinition
-  ): Function | ValidatorDefinition | void {
+    def?: ValidatorAsset
+  ): ValidatorAsset|void {
     if (def === undefined) {
       return Vue.options['validators'][id]
     } else {
:shirt: refactor(asset): update flowtype