diff --git a/crates/cargo-test-macro/src/lib.rs b/crates/cargo-test-macro/src/lib.rs
index dae129ade66..11d417df8ac 100644
--- a/crates/cargo-test-macro/src/lib.rs
+++ b/crates/cargo-test-macro/src/lib.rs
@@ -31,8 +31,12 @@ pub fn cargo_test(attr: TokenStream, item: TokenStream) -> TokenStream {
             }
         };
 
-        let mut new_body =
-            to_token_stream("let _test_guard = cargo_test_support::paths::init_root();");
+        let mut new_body = to_token_stream(
+            r#"let _test_guard = {
+                let tmp_dir = option_env!("CARGO_TARGET_TMPDIR");
+                cargo_test_support::paths::init_root(tmp_dir)
+            };"#,
+        );
 
         // If this is a `build_std` test (aka `tests/build-std/*.rs`) then they
         // only run on nightly and they only run when specifically instructed to
diff --git a/crates/cargo-test-support/src/git.rs b/crates/cargo-test-support/src/git.rs
index cc6b0c7462a..18c4646b37d 100644
--- a/crates/cargo-test-support/src/git.rs
+++ b/crates/cargo-test-support/src/git.rs
@@ -132,11 +132,12 @@ pub fn init(path: &Path) -> git2::Repository {
 }
 
 fn default_search_path() {
-    use crate::paths::GLOBAL_ROOT;
+    use crate::paths::global_root;
     use git2::{opts::set_search_path, ConfigLevel};
+
     static INIT: Once = Once::new();
     INIT.call_once(|| unsafe {
-        let path = GLOBAL_ROOT.join("blank_git_search_path");
+        let path = global_root().join("blank_git_search_path");
         t!(set_search_path(ConfigLevel::System, &path));
         t!(set_search_path(ConfigLevel::Global, &path));
         t!(set_search_path(ConfigLevel::XDG, &path));
diff --git a/crates/cargo-test-support/src/paths.rs b/crates/cargo-test-support/src/paths.rs
index 6e0dbf9d68b..192657dae58 100644
--- a/crates/cargo-test-support/src/paths.rs
+++ b/crates/cargo-test-support/src/paths.rs
@@ -14,28 +14,44 @@ use std::sync::Mutex;
 static CARGO_INTEGRATION_TEST_DIR: &str = "cit";
 
 lazy_static! {
-    pub static ref GLOBAL_ROOT: PathBuf = {
-        let mut path = t!(env::current_exe());
-        path.pop(); // chop off exe name
-        path.pop(); // chop off 'debug'
-
-        // If `cargo test` is run manually then our path looks like
-        // `target/debug/foo`, in which case our `path` is already pointing at
-        // `target`. If, however, `cargo test --target $target` is used then the
-        // output is `target/$target/debug/foo`, so our path is pointing at
-        // `target/$target`. Here we conditionally pop the `$target` name.
-        if path.file_name().and_then(|s| s.to_str()) != Some("target") {
-            path.pop();
-        }
-
-        path.push(CARGO_INTEGRATION_TEST_DIR);
-        path.mkdir_p();
-        path
-    };
+    // TODO: Use `SyncOnceCell` when stable
+    static ref GLOBAL_ROOT: Mutex<Option<PathBuf>> = Mutex::new(None);
 
     static ref TEST_ROOTS: Mutex<HashMap<String, PathBuf>> = Default::default();
 }
 
+/// This is used when running cargo is pre-CARGO_TARGET_TMPDIR
+/// TODO: Remove when CARGO_TARGET_TMPDIR grows old enough.
+fn global_root_legacy() -> PathBuf {
+    let mut path = t!(env::current_exe());
+    path.pop(); // chop off exe name
+    path.pop(); // chop off "deps"
+    path.push("tmp");
+    path.mkdir_p();
+    path
+}
+
+fn set_global_root(tmp_dir: Option<&'static str>) {
+    let mut lock = GLOBAL_ROOT.lock().unwrap();
+    if lock.is_none() {
+        let mut root = match tmp_dir {
+            Some(tmp_dir) => PathBuf::from(tmp_dir),
+            None => global_root_legacy(),
+        };
+
+        root.push(CARGO_INTEGRATION_TEST_DIR);
+        *lock = Some(root);
+    }
+}
+
+pub fn global_root() -> PathBuf {
+    let lock = GLOBAL_ROOT.lock().unwrap();
+    match lock.as_ref() {
+        Some(p) => p.clone(),
+        None => unreachable!("GLOBAL_ROOT not set yet"),
+    }
+}
+
 // We need to give each test a unique id. The test name could serve this
 // purpose, but the `test` crate doesn't have a way to obtain the current test
 // name.[*] Instead, we used the `cargo-test-macro` crate to automatically
@@ -52,14 +68,15 @@ pub struct TestIdGuard {
     _private: (),
 }
 
-pub fn init_root() -> TestIdGuard {
+pub fn init_root(tmp_dir: Option<&'static str>) -> TestIdGuard {
     static NEXT_ID: AtomicUsize = AtomicUsize::new(0);
 
-    let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
+    let id = NEXT_ID.fetch_add(1, Ordering::SeqCst);
     TEST_ID.with(|n| *n.borrow_mut() = Some(id));
 
     let guard = TestIdGuard { _private: () };
 
+    set_global_root(tmp_dir);
     let r = root();
     r.rm_rf();
     r.mkdir_p();
@@ -80,7 +97,10 @@ pub fn root() -> PathBuf {
              order to be able to use the crate root.",
         )
     });
-    GLOBAL_ROOT.join(&format!("t{}", id))
+
+    let mut root = global_root();
+    root.push(&format!("t{}", id));
+    root
 }
 
 pub fn home() -> PathBuf {