diff --git a/docs/tutorial.it-IT.md b/docs/tutorial.it-IT.md
index 7153c7d90..f0bd8270d 100755
--- a/docs/tutorial.it-IT.md
+++ b/docs/tutorial.it-IT.md
@@ -327,7 +327,7 @@ var CommentList = React.createClass({
   render: function() {
     var commentNodes = this.props.data.map(function (comment) {
       return (
-        <Comment author={comment.author}>
+        <Comment author={comment.author} key={comment.id}>
           {comment.text}
         </Comment>
       );
diff --git a/docs/tutorial.ja-JP.md b/docs/tutorial.ja-JP.md
index 12a961764..aeab726d5 100755
--- a/docs/tutorial.ja-JP.md
+++ b/docs/tutorial.ja-JP.md
@@ -324,7 +324,7 @@ var CommentList = React.createClass({
   render: function() {
     var commentNodes = this.props.data.map(function (comment) {
       return (
-        <Comment author={comment.author}>
+        <Comment author={comment.author} key={comment.id}>
           {comment.text}
         </Comment>
       );
diff --git a/docs/tutorial.ko-KR.md b/docs/tutorial.ko-KR.md
index 113bd0f70..b1b8d1348 100755
--- a/docs/tutorial.ko-KR.md
+++ b/docs/tutorial.ko-KR.md
@@ -331,7 +331,7 @@ var CommentList = React.createClass({
   render: function() {
     var commentNodes = this.props.data.map(function (comment) {
       return (
-        <Comment author={comment.author}>
+        <Comment author={comment.author} key={comment.id}>
           {comment.text}
         </Comment>
       );