diff --git a/Cargo.lock b/Cargo.lock
index 7b02cc6da..1778b4fcd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1919,6 +1919,7 @@ dependencies = [
  "dirs 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "env_logger 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "failure 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "fs2 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "fs_extra 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "openssl 0.10.23 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/Cargo.toml b/Cargo.toml
index 334f1717b..ff65929f5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,6 +27,7 @@ toml = "0.5.0"
 uuid = "0.7"
 which = "2.0.1"
 rand = "0.6.5"
+fs2 = "0.4.3"
 
 [dev-dependencies]
 assert_cmd = "0.11.1"
diff --git a/src/wranglerjs/mod.rs b/src/wranglerjs/mod.rs
index 4b4989dfb..9ffa5881a 100644
--- a/src/wranglerjs/mod.rs
+++ b/src/wranglerjs/mod.rs
@@ -1,6 +1,7 @@
 use crate::commands::publish::package::Package;
 use crate::install;
 use binary_install::Cache;
+use fs2::FileExt;
 use log::info;
 use rand::distributions::Alphanumeric;
 use rand::{thread_rng, Rng};
@@ -191,6 +192,11 @@ pub fn run_build(
 // Run {npm install} in the specified directory. Skips the install if a
 // {node_modules} is found in the directory.
 pub fn run_npm_install(dir: PathBuf) -> Result<(), failure::Error> {
+    let flock_path = dir.join(&".install.lock");
+    let flock = File::create(&flock_path)?;
+    // avoid running multiple {npm install} at the same time (eg. in tests)
+    flock.lock_exclusive()?;
+
     if dir.join("node_modules").exists() {
         info!("skipping npm install because node_modules exists");
         return Ok(());
@@ -202,6 +208,10 @@ pub fn run_npm_install(dir: PathBuf) -> Result<(), failure::Error> {
     info!("Running {:?} in directory {:?}", command, dir);
 
     let status = command.status()?;
+
+    flock.unlock()?;
+    fs::remove_file(&flock_path)?;
+
     if status.success() {
         Ok(())
     } else {