diff --git a/Cargo.lock b/Cargo.lock
index 9da3f79141d..30ff38707f2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6,6 +6,7 @@ dependencies = [
  "env_logger 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "jsonrpc-core 7.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "languageserver-types 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "racer 2.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "rls-analysis 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/Cargo.toml b/Cargo.toml
index 23483a866df..6f833fb0909 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,7 +12,9 @@ build = "build.rs"
 [dependencies]
 cargo = { git = "https://github.com/rust-lang/cargo" }
 env_logger = "0.4"
+jsonrpc-core = "7.0.1"
 languageserver-types = "0.12"
+lazy_static = "0.2"
 log = "0.3"
 racer = "2.0.6"
 rls-analysis = "0.4.5"
@@ -26,4 +28,3 @@ serde_derive = "1.0"
 toml = "0.4"
 url = "1.1.0"
 url_serde = "0.2.0"
-jsonrpc-core = "7.0.1"
diff --git a/src/build/mod.rs b/src/build/mod.rs
index 6d6f2f3e83c..93cdfba541c 100644
--- a/src/build/mod.rs
+++ b/src/build/mod.rs
@@ -19,11 +19,12 @@ use std::ffi::OsString;
 use std::io::{self, Write};
 use std::mem;
 use std::path::{Path, PathBuf};
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, MutexGuard};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::thread;
 use std::time::Duration;
 
+
 mod cargo;
 mod rustc;
 
@@ -409,15 +410,24 @@ impl Write for BufWriter {
     }
 }
 
+
+// Ensures we don't race on the env vars. This is only likely in tests, where we
+// have multiple copies of the RLS running in the same process.
+lazy_static! {
+    static ref ENV_LOCK: Mutex<()> = Mutex::new(());
+}
+
 // An RAII helper to set and reset the current working directory and env vars.
-struct Environment {
+struct Environment<'a> {
     old_vars: HashMap<String, Option<OsString>>,
+    _guard: MutexGuard<'a, ()>,
 }
 
-impl Environment {
-    fn push(envs: &HashMap<String, Option<OsString>>) -> Environment {
+impl<'a> Environment<'a> {
+    fn push(envs: &HashMap<String, Option<OsString>>) -> Environment<'a> {
         let mut result = Environment {
             old_vars: HashMap::new(),
+            _guard: ENV_LOCK.lock().unwrap(),
         };
 
         for (k, v) in envs {
@@ -435,7 +445,7 @@ impl Environment {
     }
 }
 
-impl Drop for Environment {
+impl<'a> Drop for Environment<'a> {
     fn drop(&mut self) {
         for (k, v) in &self.old_vars {
             match *v {
diff --git a/src/build/rustc.rs b/src/build/rustc.rs
index 967cc0df212..ae903a1fd53 100644
--- a/src/build/rustc.rs
+++ b/src/build/rustc.rs
@@ -36,6 +36,7 @@ use std::io;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
 
+
 // Runs a single instance of rustc. Runs in-process.
 pub fn rustc(vfs: &Vfs, args: &[String], envs: &HashMap<String, Option<OsString>>, build_dir: &Path, rls_config: Arc<Mutex<Config>>) -> BuildResult {
     trace!("rustc - args: `{:?}`, envs: {:?}, build dir: {:?}", args, envs, build_dir);
@@ -47,6 +48,7 @@ pub fn rustc(vfs: &Vfs, args: &[String], envs: &HashMap<String, Option<OsString>
     if rls_config.lock().unwrap().clear_env_rust_log {
         local_envs.insert(String::from("RUST_LOG"), None);
     }
+
     let _restore_env = Environment::push(&local_envs);
     let buf = Arc::new(Mutex::new(vec![]));
     let err_buf = buf.clone();
diff --git a/src/main.rs b/src/main.rs
index 9a45a9717b4..e6fe37a6cf8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,8 @@ extern crate cargo;
 extern crate env_logger;
 extern crate languageserver_types as ls_types;
 #[macro_use]
+extern crate lazy_static;
+#[macro_use]
 extern crate log;
 extern crate racer;
 extern crate rls_analysis as analysis;
diff --git a/src/test/harness.rs b/src/test/harness.rs
index d23c4d3538c..b5de6f64b65 100644
--- a/src/test/harness.rs
+++ b/src/test/harness.rs
@@ -25,7 +25,7 @@ use serde_json;
 use server::{self as ls_server, ServerMessage};
 use vfs;
 
-const TEST_TIMEOUT_IN_SEC: u64 = 60;
+const TEST_TIMEOUT_IN_SEC: u64 = 240;
 
 // Initialise and run the internals of an LS protocol RLS server.
 pub fn mock_server(messages: Vec<ServerMessage>) -> (ls_server::LsService<RecordOutput>, LsResultList)