diff --git a/README.md b/README.md
index 2d59d4716e..88c985311b 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,9 @@ A library to **sub**mit e**xt**rinsics to a [substrate](https://github.com/parit
 
 See [examples](./examples).
 
+If you use `#[derive(Call)]` without `#[module]` in the same module, you will get errors
+complaining about an undefined method with a name starting with `with_`.
+
 **Alternatives**
 
 [substrate-api-client](https://github.com/scs/substrate-api-client) provides similar functionality.