diff --git a/eden/scm/lib/revisionstore/Cargo.toml b/eden/scm/lib/revisionstore/Cargo.toml
index 64cc467535..caeacfa1bc 100644
--- a/eden/scm/lib/revisionstore/Cargo.toml
+++ b/eden/scm/lib/revisionstore/Cargo.toml
@@ -52,9 +52,10 @@ util = { path = "../util" }
 zstd = { version = "0.5" }
 
 [dev-dependencies]
+lazy_static = "1.3.0"
 maplit = "1.0"
-rand_chacha = "0.2"
 quickcheck = "0.9"
+rand_chacha = "0.2"
 types = { path = "../types", default-features = false, features = ["for-tests"] }
 
 [lib]
diff --git a/eden/scm/lib/revisionstore/src/contentstore.rs b/eden/scm/lib/revisionstore/src/contentstore.rs
index 3022bea3a6..3168e87016 100644
--- a/eden/scm/lib/revisionstore/src/contentstore.rs
+++ b/eden/scm/lib/revisionstore/src/contentstore.rs
@@ -1028,6 +1028,8 @@ mod tests {
 
         #[test]
         fn test_lfs_remote() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let localdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -1136,6 +1138,8 @@ mod tests {
 
         #[test]
         fn test_lfs_prefetch_once() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let localdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
diff --git a/eden/scm/lib/revisionstore/src/lfs.rs b/eden/scm/lib/revisionstore/src/lfs.rs
index bac01be4df..3fd28fed47 100644
--- a/eden/scm/lib/revisionstore/src/lfs.rs
+++ b/eden/scm/lib/revisionstore/src/lfs.rs
@@ -2192,10 +2192,12 @@ mod tests {
     #[cfg(feature = "fb")]
     mod fb_test {
         use super::*;
+        use parking_lot::Mutex;
         use std::env::set_var;
 
         #[test]
-        fn test_lfs_non_present() -> Result<()> {
+        fn test_lfs_proxy_non_present() -> Result<()> {
+            let _env_lock = crate::env_lock();
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2225,6 +2227,8 @@ mod tests {
         #[test]
         #[cfg(not(windows))]
         fn test_lfs_proxy_no_http() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2244,7 +2248,9 @@ mod tests {
 
             let objs = [(blob.0, blob.1)].iter().cloned().collect::<HashSet<_>>();
             let resp = remote.batch_fetch(&objs, |_, _| unreachable!());
-            assert!(resp.unwrap_err().to_string().contains("Proxy"));
+            // ex. [56] Failure when receiving data from the peer (Proxy CONNECT aborted)
+            // But not necessarily that message in all cases.
+            assert!(resp.is_err());
 
             Ok(())
         }
@@ -2252,6 +2258,8 @@ mod tests {
         #[test]
         #[cfg(not(windows))]
         fn test_lfs_proxy_http() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2271,13 +2279,15 @@ mod tests {
 
             let objs = [(blob.0, blob.1)].iter().cloned().collect::<HashSet<_>>();
             let resp = remote.batch_fetch(&objs, |_, _| unreachable!());
-            assert!(resp.unwrap_err().to_string().contains("Proxy"));
+            assert!(resp.is_err());
 
             Ok(())
         }
 
         #[test]
         fn test_lfs_no_proxy() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2312,6 +2322,8 @@ mod tests {
 
         #[test]
         fn test_lfs_no_proxy_suffix() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2343,6 +2355,8 @@ mod tests {
 
         #[test]
         fn test_lfs_remote() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2389,6 +2403,8 @@ mod tests {
 
         #[test]
         fn test_lfs_request_timeout() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let mut config = make_lfs_config(&cachedir);
@@ -2415,6 +2431,8 @@ mod tests {
 
         #[test]
         fn test_lfs_remote_datastore() -> Result<()> {
+            let _env_lock = crate::env_lock();
+
             let cachedir = TempDir::new()?;
             let lfsdir = TempDir::new()?;
             let config = make_lfs_config(&cachedir);
@@ -2463,6 +2481,8 @@ mod tests {
 
     #[test]
     fn test_lfs_remote_file() -> Result<()> {
+        let _env_lock = crate::env_lock();
+
         let cachedir = TempDir::new()?;
         let mut config = make_lfs_config(&cachedir);
 
@@ -2516,6 +2536,8 @@ mod tests {
 
     #[test]
     fn test_lfs_upload_remote_file() -> Result<()> {
+        let _env_lock = crate::env_lock();
+
         let cachedir = TempDir::new()?;
         let mut config = make_lfs_config(&cachedir);
 
@@ -2560,6 +2582,8 @@ mod tests {
 
     #[test]
     fn test_lfs_upload_move_to_shared() -> Result<()> {
+        let _env_lock = crate::env_lock();
+
         let cachedir = TempDir::new()?;
         let mut config = make_lfs_config(&cachedir);
 
diff --git a/eden/scm/lib/revisionstore/src/lib.rs b/eden/scm/lib/revisionstore/src/lib.rs
index f332dc5753..f9801e4bc8 100644
--- a/eden/scm/lib/revisionstore/src/lib.rs
+++ b/eden/scm/lib/revisionstore/src/lib.rs
@@ -191,3 +191,30 @@ pub use revisionstore_types::*;
 
 #[cfg(any(test, feature = "for-tests"))]
 pub mod testutil;
+
+#[cfg(test)]
+mod env_lock {
+    use lazy_static::lazy_static;
+    use parking_lot::Mutex;
+
+    lazy_static! {
+        pub static ref ENV_LOCK: Mutex<()> = Mutex::new(());
+    }
+
+    fn env_reset() {
+        for name in ["https_proxy", "http_proxy", "NO_PROXY"].iter() {
+            if std::env::var_os(name).is_some() {
+                std::env::remove_var(name)
+            }
+        }
+    }
+
+    pub(crate) fn env_lock() -> impl Drop {
+        let lock = ENV_LOCK.lock();
+        env_reset();
+        lock
+    }
+}
+
+#[cfg(test)]
+pub(crate) use env_lock::env_lock;