diff --git a/components/style/lib.rs b/components/style/lib.rs
index a19b530b9b1..6d576c842de 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -32,6 +32,8 @@
 #![cfg_attr(feature = "servo", plugin(heapsize_plugin))]
 #![cfg_attr(feature = "servo", plugin(plugins))]
 
+#![deny(warnings)]
+
 // FIXME(bholley): We need to blanket-allow unsafe code in order to make the
 // gecko atom!() macro work. When Rust 1.14 is released [1], we can uncomment
 // the commented-out attributes in regen_atoms.py and go back to denying unsafe
diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index cdfca9b8653..39e89f0742f 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#![deny(warnings)]
 
 #[macro_use]extern crate style;
 extern crate app_units;