diff --git a/lib/chai/core/assertions.js b/lib/chai/core/assertions.js
index f34e2f512..c398ab8e2 100644
--- a/lib/chai/core/assertions.js
+++ b/lib/chai/core/assertions.js
@@ -291,7 +291,7 @@ module.exports = function (chai, _) {
    * Asserts that the target is `null`.
    *
    *     expect(null).to.be.null;
-   *     expect(undefined).not.to.be.null;
+   *     expect(undefined).to.not.be.null;
    *
    * @name null
    * @api public