diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index f6b73f037f2..c2363c9946a 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -107,6 +107,7 @@
 #![feature(macro_rules, globs, linkage)]
 #![feature(default_type_params, phase, lang_items, unsafe_destructor)]
 #![feature(import_shadowing, slicing_syntax)]
+#![feature(unboxed_closures)]
 
 // Don't link to std. We are std.
 #![no_std]