diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 9bb3e79744bb6..39c7a37501121 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -9,6 +9,7 @@ dependencies = [
  "getopts 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "kernel32-sys 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "md5 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.1.28 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -59,6 +60,11 @@ name = "libc"
 version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "md5"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "num_cpus"
 version = "0.2.11"
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index 7b379e1c7b6b9..f9a64567ffde0 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -31,3 +31,4 @@ winapi = "0.2"
 kernel32-sys = "0.2"
 gcc = "0.3.17"
 libc = "0.2"
+md5 = "0.1"
diff --git a/src/bootstrap/build/channel.rs b/src/bootstrap/build/channel.rs
index 5c39356d214df..611e3475610a7 100644
--- a/src/bootstrap/build/channel.rs
+++ b/src/bootstrap/build/channel.rs
@@ -8,15 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::env;
 use std::fs::{self, File};
 use std::io::prelude::*;
-use std::path::Path;
 use std::process::Command;
 
 use build_helper::output;
+use md5;
 
 use build::Build;
-use build::util::mtime;
 
 pub fn collect(build: &mut Build) {
     let mut main_mk = String::new();
@@ -80,7 +80,8 @@ pub fn collect(build: &mut Build) {
         build.short_ver_hash = Some(short_ver_hash);
     }
 
-    build.bootstrap_key = mtime(Path::new("config.toml")).seconds()
-                                                        .to_string();
+    let key = md5::compute(build.release.as_bytes());
+    build.bootstrap_key = format!("{:02x}{:02x}{:02x}{:02x}",
+                                  key[0], key[1], key[2], key[3]);
+    env::set_var("RUSTC_BOOTSTRAP_KEY", &build.bootstrap_key);
 }
-
diff --git a/src/bootstrap/main.rs b/src/bootstrap/main.rs
index 32432132c1730..bf29ac107ffbf 100644
--- a/src/bootstrap/main.rs
+++ b/src/bootstrap/main.rs
@@ -20,6 +20,7 @@ extern crate libc;
 extern crate num_cpus;
 extern crate rustc_serialize;
 extern crate toml;
+extern crate md5;
 
 use std::env;
 
diff --git a/src/rustc/Cargo.lock b/src/rustc/Cargo.lock
index 4b5c2850dab08..a3420d75218fb 100644
--- a/src/rustc/Cargo.lock
+++ b/src/rustc/Cargo.lock
@@ -73,7 +73,7 @@ dependencies = [
  "rbml 0.0.0",
  "rustc_back 0.0.0",
  "rustc_bitflags 0.0.0",
- "rustc_const_eval 0.0.0",
+ "rustc_const_math 0.0.0",
  "rustc_data_structures 0.0.0",
  "serialize 0.0.0",
  "syntax 0.0.0",
@@ -106,6 +106,19 @@ dependencies = [
 [[package]]
 name = "rustc_const_eval"
 version = "0.0.0"
+dependencies = [
+ "graphviz 0.0.0",
+ "log 0.0.0",
+ "rustc 0.0.0",
+ "rustc_back 0.0.0",
+ "rustc_const_math 0.0.0",
+ "serialize 0.0.0",
+ "syntax 0.0.0",
+]
+
+[[package]]
+name = "rustc_const_math"
+version = "0.0.0"
 dependencies = [
  "log 0.0.0",
  "serialize 0.0.0",
@@ -131,6 +144,8 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_back 0.0.0",
  "rustc_borrowck 0.0.0",
+ "rustc_const_eval 0.0.0",
+ "rustc_incremental 0.0.0",
  "rustc_lint 0.0.0",
  "rustc_llvm 0.0.0",
  "rustc_metadata 0.0.0",
@@ -147,6 +162,19 @@ dependencies = [
  "syntax_ext 0.0.0",
 ]
 
+[[package]]
+name = "rustc_incremental"
+version = "0.0.0"
+dependencies = [
+ "graphviz 0.0.0",
+ "log 0.0.0",
+ "rbml 0.0.0",
+ "rustc 0.0.0",
+ "rustc_data_structures 0.0.0",
+ "serialize 0.0.0",
+ "syntax 0.0.0",
+]
+
 [[package]]
 name = "rustc_lint"
 version = "0.0.0"
@@ -154,6 +182,7 @@ dependencies = [
  "log 0.0.0",
  "rustc 0.0.0",
  "rustc_back 0.0.0",
+ "rustc_const_eval 0.0.0",
  "syntax 0.0.0",
 ]
 
@@ -176,7 +205,7 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_back 0.0.0",
  "rustc_bitflags 0.0.0",
- "rustc_const_eval 0.0.0",
+ "rustc_const_math 0.0.0",
  "rustc_llvm 0.0.0",
  "serialize 0.0.0",
  "syntax 0.0.0",
@@ -191,6 +220,7 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_back 0.0.0",
  "rustc_const_eval 0.0.0",
+ "rustc_const_math 0.0.0",
  "rustc_data_structures 0.0.0",
  "syntax 0.0.0",
 ]
@@ -201,6 +231,7 @@ version = "0.0.0"
 dependencies = [
  "log 0.0.0",
  "rustc 0.0.0",
+ "rustc_const_eval 0.0.0",
  "syntax 0.0.0",
 ]
 
@@ -247,7 +278,6 @@ version = "0.0.0"
 dependencies = [
  "log 0.0.0",
  "rustc 0.0.0",
- "rustc_front 0.0.0",
  "syntax 0.0.0",
 ]
 
@@ -262,7 +292,9 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_back 0.0.0",
  "rustc_const_eval 0.0.0",
+ "rustc_const_math 0.0.0",
  "rustc_data_structures 0.0.0",
+ "rustc_incremental 0.0.0",
  "rustc_llvm 0.0.0",
  "rustc_mir 0.0.0",
  "rustc_platform_intrinsics 0.0.0",
@@ -280,6 +312,7 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_back 0.0.0",
  "rustc_const_eval 0.0.0",
+ "rustc_const_math 0.0.0",
  "rustc_platform_intrinsics 0.0.0",
  "syntax 0.0.0",
 ]
@@ -294,6 +327,7 @@ dependencies = [
  "log 0.0.0",
  "rustc 0.0.0",
  "rustc_back 0.0.0",
+ "rustc_const_eval 0.0.0",
  "rustc_driver 0.0.0",
  "rustc_lint 0.0.0",
  "rustc_metadata 0.0.0",