diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index f3d9246c6fc6..5cba65f7f0ad 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -113,7 +113,7 @@
 //! More documentation can be found in each respective module below, and you can
 //! also check out the `src/bootstrap/README.md` file for more information.
 
-//#![deny(warnings)]
+#![deny(warnings)]
 #![feature(core_intrinsics)]
 
 #[macro_use]