diff --git a/demo02/index.html b/demo02/index.html
index c0690997..48c6c9ec 100644
--- a/demo02/index.html
+++ b/demo02/index.html
@@ -13,8 +13,8 @@
       ReactDOM.render(
         <div>
         {
-          names.map(function (name) {
-            return <div>Hello, {name}!</div>
+          names.map(function (name, index) {
+            return <div key={index}>Hello, {name}!</div>
           })
         }
         </div>,
diff --git a/demo03/index.html b/demo03/index.html
index 4898c4f4..7c0645b8 100644
--- a/demo03/index.html
+++ b/demo03/index.html
@@ -9,8 +9,8 @@
     <div id="example"></div>
     <script type="text/babel">
       var arr = [
-        <h1>Hello world!</h1>,
-        <h2>React is awesome</h2>,
+        <h1 key="1">Hello world!</h1>,
+        <h2 key="2">React is awesome</h2>,
       ];
       ReactDOM.render(
         <div>{arr}</div>,