diff --git a/src/rustbook/main.rs b/src/rustbook/main.rs
index ace57f0ac2c0..9bcfc7f45d34 100644
--- a/src/rustbook/main.rs
+++ b/src/rustbook/main.rs
@@ -12,7 +12,6 @@
 #![feature(collections)]
 #![feature(core)]
 #![feature(old_io)]
-#![feature(os)]
 #![feature(env)]
 #![feature(old_path)]
 #![feature(rustdoc)]