diff --git a/readme.md b/readme.md
index b15b3632..9c36ce3c 100644
--- a/readme.md
+++ b/readme.md
@@ -140,6 +140,7 @@ Legion provides a few feature flags:
 * `extended-tuple-impls` - Extends the maximum size of view and component tuples from 8 to 24, at the cost of increased compile times. Off by default.
 * `serialize` - Enables the serde serialization module and associated functionality. Enabled by default.
 * `crossbeam-events` - Implements the `EventSender` trait for crossbeam `Sender` channels, allowing them to be used for event subscriptions. Enabled by default.
+* `codegen` - Enables the `#[system]` procedural macro. Enabled by default.
 
 ## WASM