diff --git a/README.md b/README.md
index 335743d2..5507cc6e 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,12 @@ The `bodyParser` object exposes various factories to create middlewares. All
 middlewares will populate the `req.body` property with the parsed body when
 the `Content-Type` request header matches the `type` option.
 
+**Note** As of v2, `req.body` is left `undefined` when no body is parsed (for
+example when the request has neither `Content-Length` nor `Transfer-Encoding`,
+or when `Content-Type` does not match). In v1, `req.body` was always initialized
+to `{}`. Code that assumes `req.body` is always an object should use optional
+chaining (for example `req.body?.username`) or set a default.
+
 The various errors returned by this module are described in the
 [errors section](#errors).