diff --git a/src/librustc/back/passes.rs b/src/librustc/back/passes.rs
index 2e304b93c7e4..cc9fe5771591 100644
--- a/src/librustc/back/passes.rs
+++ b/src/librustc/back/passes.rs
@@ -9,6 +9,8 @@
 // except according to those terms.
 
 use core::prelude::*;
+use core::str;
+use core::io;
 
 use driver::session::{OptLevel, No, Less, Default, Aggressive};
 use driver::session::{Session};