diff --git a/.gitmodules b/.gitmodules
index 50ed51e..a71118f 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,6 +1,3 @@
-[submodule "compiler-rt"]
-	path = compiler-rt
-	url = https://github.com/rust-lang/compiler-rt
 [submodule "libm"]
 	path = libm
 	url = https://github.com/rust-lang-nursery/libm
diff --git a/build.rs b/build.rs
index be5d42b..c714bc1 100644
--- a/build.rs
+++ b/build.rs
@@ -76,7 +76,7 @@ mod c {
 
     use std::collections::BTreeMap;
     use std::env;
-    use std::path::Path;
+    use std::path::PathBuf;
 
     struct Sources {
         // SYMBOL -> PATH TO SOURCE
@@ -411,15 +411,19 @@ mod c {
             sources.remove(&["__aeabi_cdcmp", "__aeabi_cfcmp"]);
         }
 
-        // When compiling in rustbuild (the rust-lang/rust repo) this build
-        // script runs from a directory other than this root directory.
-        let root = if cfg!(feature = "rustbuild") {
-            Path::new("../../libcompiler_builtins")
-        } else {
-            Path::new(".")
+        // When compiling the C code we require the user to tell us where the
+        // source code is, and this is largely done so when we're compiling as
+        // part of rust-lang/rust we can use the same llvm-project repository as
+        // rust-lang/rust.
+        let root = match env::var_os("RUST_COMPILER_RT_ROOT") {
+            Some(s) => PathBuf::from(s),
+            None => panic!("RUST_COMPILER_RT_ROOT is not set"),
         };
+        if !root.exists() {
+            panic!("RUST_COMPILER_RT_ROOT={} does not exist", root.display());
+        }
 
-        let src_dir = root.join("compiler-rt/lib/builtins");
+        let src_dir = root.join("lib/builtins");
         for (sym, src) in sources.map.iter() {
             let src = src_dir.join(src);
             cfg.file(&src);
diff --git a/ci/azure-steps.yml b/ci/azure-steps.yml
index c8a9540..f08beca 100644
--- a/ci/azure-steps.yml
+++ b/ci/azure-steps.yml
@@ -4,13 +4,15 @@ steps:
 
   - template: azure-install-rust.yml
 
-  - script: rustup component add rust-src
-    displayName: Install Rust sources
-    condition: eq( variables['XARGO'], '1' )
-
   - bash: rustup target add $TARGET
     displayName: Install Rust target
-    condition: ne( variables['XARGO'], '1' )
+
+  - bash: |
+      set -e
+      curl -L https://github.com/rust-lang/llvm-project/archive/rustc/8.0-2019-03-18.tar.gz | \
+        tar xzf - --strip-components 1 llvm-project-rustc-8.0-2019-03-18/compiler-rt
+      echo '##vso[task.setvariable variable=RUST_COMPILER_RT_ROOT]./compiler-rt'
+    displayName: "Download compiler-rt reference sources"
 
   - bash: ./ci/run.sh $TARGET
     condition: ne( variables['Agent.OS'], 'Linux' )
diff --git a/ci/run-docker.sh b/ci/run-docker.sh
index ddb970c..dbc86ca 100755
--- a/ci/run-docker.sh
+++ b/ci/run-docker.sh
@@ -18,6 +18,7 @@ run() {
            --user $(id -u):$(id -g) \
            -e CARGO_HOME=/cargo \
            -e CARGO_TARGET_DIR=/target \
+           -e RUST_COMPILER_RT_ROOT \
            -v $HOME/.cargo:/cargo \
            -v `pwd`/target:/target \
            -v `pwd`:/checkout:ro \
diff --git a/ci/run.sh b/ci/run.sh
index 4d6d6c6..ae32806 100755
--- a/ci/run.sh
+++ b/ci/run.sh
@@ -1,6 +1,5 @@
 set -ex
 
-export CARGO_INCREMENTAL=0
 cargo=cargo
 
 # Test our implementation
diff --git a/compiler-rt b/compiler-rt
deleted file mode 160000
index 03fc28f..0000000
--- a/compiler-rt
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 03fc28f9273eeab16f1005f982dfde5900bddb29