diff --git a/src/libserialize/tests/json.rs b/src/libserialize/tests/json.rs
index 3fb6bda679b..0fe3d4cfd62 100644
--- a/src/libserialize/tests/json.rs
+++ b/src/libserialize/tests/json.rs
@@ -1,3 +1,4 @@
+#[allow(unused_extern_crates)]
 extern crate serialize as rustc_serialize;
 
 use rustc_serialize::{Encodable, Decodable};
diff --git a/src/libserialize/tests/opaque.rs b/src/libserialize/tests/opaque.rs
index fff6fc69e78..62a8f251244 100644
--- a/src/libserialize/tests/opaque.rs
+++ b/src/libserialize/tests/opaque.rs
@@ -1,3 +1,4 @@
+#[allow(unused_extern_crates)]
 extern crate serialize as rustc_serialize;
 
 use rustc_serialize::{Encodable, Decodable};