diff --git a/src/api/action.ts b/src/api/action.ts
index cc5a4ed57..708b52be1 100644
--- a/src/api/action.ts
+++ b/src/api/action.ts
@@ -33,13 +33,13 @@ export interface IActionFactory {
     <T extends Function>(name: string, fn: T): T & IAction
 
     // named decorator
-    (customName: string): (target: Object, key: string, baseDescriptor?: PropertyDescriptor) => void
+    (customName: string): (target: Object, key: string | symbol, baseDescriptor?: PropertyDescriptor) => void
 
     // unnamed decorator
-    (target: Object, propertyKey: string, descriptor?: PropertyDescriptor): void
+    (target: Object, propertyKey: string | symbol, descriptor?: PropertyDescriptor): void
 
     // @action.bound decorator
-    bound(target: Object, propertyKey: string, descriptor?: PropertyDescriptor): void
+    bound(target: Object, propertyKey: string | symbol, descriptor?: PropertyDescriptor): void
 }
 
 export var action: IActionFactory = function action(arg1, arg2?, arg3?, arg4?): any {
diff --git a/src/api/observabledecorator.ts b/src/api/observabledecorator.ts
index e01671416..2cb6c203e 100644
--- a/src/api/observabledecorator.ts
+++ b/src/api/observabledecorator.ts
@@ -4,7 +4,7 @@ import { IEnhancer } from "../types/modifiers"
 import { createPropDecorator, BabelDescriptor } from "../utils/decorators2"
 
 export type IObservableDecorator = {
-    (target: Object, property: string, descriptor?: PropertyDescriptor): void
+    (target: Object, property: string | symbol, descriptor?: PropertyDescriptor): void
     enhancer: IEnhancer<any>
 }
 
diff --git a/test/base/decorate.js b/test/base/decorate.js
index 8fec69602..7aea6fe64 100644
--- a/test/base/decorate.js
+++ b/test/base/decorate.js
@@ -50,7 +50,7 @@ test("decorate should work", function() {
     }
 
     decorate(Box, {
-        uninitialized: observable,
+        uninitialized: observable.ref,
         undeclared: observable,
         height: observable,
         sizes: observable,
@@ -97,6 +97,7 @@ test("decorate should work", function() {
 
 test("decorate should work with plain object", function() {
     const box = {
+        /** @type {boolean | undefined} */
         uninitialized: undefined,
         height: 20,
         sizes: [2],