diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index f77b4d7461e..ce7ddffd825 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -134,6 +134,7 @@
 #![feature(const_type_id)]
 #![feature(const_caller_location)]
 #![cfg_attr(bootstrap, feature(slice_patterns))]
+#![feature(assoc_int_consts)]
 
 #[prelude_import]
 #[allow(unused)]
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index dc93ac90482..bc07c6b487b 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -237,6 +237,7 @@
 #![feature(arbitrary_self_types)]
 #![feature(array_error_internals)]
 #![feature(asm)]
+#![feature(assoc_int_consts)]
 #![feature(associated_type_bounds)]
 #![feature(box_syntax)]
 #![feature(c_variadic)]