diff --git a/src/libserialize/tests/json.rs b/src/libserialize/tests/json.rs
index 3fb6bda679b..8342e4f9742 100644
--- a/src/libserialize/tests/json.rs
+++ b/src/libserialize/tests/json.rs
@@ -1,3 +1,5 @@
+#![allow(rustc::default_hash_types)]
+
 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..26b113699c6 100644
--- a/src/libserialize/tests/opaque.rs
+++ b/src/libserialize/tests/opaque.rs
@@ -1,3 +1,5 @@
+#![allow(rustc::default_hash_types)]
+
 extern crate serialize as rustc_serialize;
 
 use rustc_serialize::{Encodable, Decodable};