diff --git a/env/src/lib.rs b/env/src/lib.rs
index 295c2ee..6d80fed 100644
--- a/env/src/lib.rs
+++ b/env/src/lib.rs
@@ -127,7 +127,7 @@
 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/env_logger/")]
-#![feature(core, env, io)]
+#![feature(core, env, old_io)]
 
 extern crate regex;
 extern crate log;