diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6e5d41b15c..073ff043da 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -233,7 +233,7 @@ p.then(function () {
 
     return "Expected exception to be thrown";
 }).then($DONE, function (e) {
-   if (!e instanceof TypeError) {
+   if (!(e instanceof TypeError)) {
       $ERROR("Expected TypeError but got " + e);
    }