diff --git a/src/index.js b/src/index.js
index 6f0fe35..0a60d3f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -21,6 +21,9 @@ function Square(props){
 
     handleClick(i) {
         const squares = this.state.squares.slice();
+        if (calculateWinner(squares) || squares[i]) {
+          return;
+        }
         squares[i] = this.state.xIsNext ? 'X' : 'O';
         this.setState(
           {