diff --git a/Makefile b/Makefile
index f1902e9..b63f815 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,8 @@
-RUST_ROOT :=
+ifdef RUST_ROOT
+	RUST_ROOT := $(RUST_ROOT)
+else
+	RUST_ROOT := /usr
+endif
 
 -include ./config.mk
 
diff --git a/main.rs b/main.rs
index 2013999..e1158be 100644
--- a/main.rs
+++ b/main.rs
@@ -1,11 +1,9 @@
-#![feature(core)]
 #![feature(core_str_ext)]
 #![feature(libc)]
 #![feature(no_std)]
 
 #![no_std]
 
-extern crate core;
 extern crate libc;
 
 #[macro_use]