diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 971991dce3d1..e9d9e4d5c5d0 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -10,6 +10,7 @@
 
 #![deny(warnings)]
 
+#![feature(ascii_ctype)]
 #![feature(box_syntax)]
 #![feature(core_float)]
 #![feature(core_private_bignum)]