diff --git a/crates/gpu/src/backend.rs b/crates/gpu/src/backend.rs
index 57e47f22e..d970003e7 100644
--- a/crates/gpu/src/backend.rs
+++ b/crates/gpu/src/backend.rs
@@ -213,12 +213,12 @@ fn disarm(marker: &std::path::Path, active: &Mutex<u32>) {
 }
 
 /// Removes the marker on the way out, a panic included (the process survived).
-struct Armed(Option<PathBuf>);
+struct Armed<'a>(Option<PathBuf>, &'a Mutex<u32>);
 
-impl Drop for Armed {
+impl Drop for Armed<'_> {
     fn drop(&mut self) {
         if let Some(m) = &self.0 {
-            disarm(m, &ACTIVE);
+            disarm(m, self.1);
         }
     }
 }
@@ -227,10 +227,16 @@ impl Drop for Armed {
 /// removing the init marker (if one is set).
 pub(crate) fn with_marker<T>(what: &str, f: impl FnOnce() -> T) -> T {
     let marker = MARKER.lock().unwrap_or_else(|e| e.into_inner()).clone();
+    with_marker_on(marker, &ACTIVE, what, f)
+}
+
+/// [`with_marker`] on an explicit marker path and scope counter (the tests use their own, so that
+/// device-creating tests running in parallel cannot join their scopes).
+fn with_marker_on<T>(marker: Option<PathBuf>, active: &Mutex<u32>, what: &str, f: impl FnOnce() -> T) -> T {
     if let Some(m) = &marker {
-        arm(m, &ACTIVE, what);
+        arm(m, active, what);
     }
-    let _armed = Armed(marker);
+    let _armed = Armed(marker, active);
     f()
 }
 
@@ -352,9 +358,6 @@ mod tests {
     }
     use super::*;
 
-    /// The tests that set the process-wide marker take turns.
-    static GLOBAL: Mutex<()> = Mutex::new(());
-
     #[test]
     fn parses_backend_names() {
         assert_eq!(parse_backends("dx12"), Some(BackendChoice::Use(Backends::DX12)));
@@ -421,13 +424,12 @@ mod tests {
 
     #[test]
     fn init_marker_is_written_during_creation_and_removed_after() {
-        let _turn = GLOBAL.lock().unwrap_or_else(|e| e.into_inner());
         let dir = std::env::temp_dir().join(format!("lc-gpu-marker-{}", std::process::id()));
         let m = dir.join("gpu-init.marker");
         let _ = std::fs::remove_dir_all(&dir);
-        set_init_marker(Some(m.clone()));
-        let seen = with_init_marker(Backends::DX12, || m.exists());
-        set_init_marker(None);
+        // a local scope counter: other tests create real devices through the process-wide one
+        let active = Mutex::new(0);
+        let seen = with_marker_on(Some(m.clone()), &active, "device creation", || m.exists());
         assert!(seen, "the marker exists while the device is created");
         assert!(!m.exists(), "and is removed afterwards");
         // a marker left behind by a crashed process is reported once; reading it leaves it in place
@@ -440,6 +442,20 @@ mod tests {
         let _ = std::fs::remove_dir_all(&dir);
     }
 
+    #[test]
+    fn with_init_marker_writes_the_process_wide_marker() {
+        let dir = std::env::temp_dir().join(format!("lc-gpu-global-{}", std::process::id()));
+        let m = dir.join("gpu-init.marker");
+        let _ = std::fs::remove_dir_all(&dir);
+        set_init_marker(Some(m.clone()));
+        let seen = with_init_marker(Backends::DX12, || m.exists());
+        set_init_marker(None);
+        // not checked for removal: device-creating tests running in parallel may still hold the file
+        // (the test above checks removal on its own scope counter)
+        assert!(seen, "the marker set with set_init_marker exists while the device is created");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     /// The window's renderer fallback: forced, remembered, the platform chain, the failed one last.
     #[test]
     fn window_renderer_fallback_order() {
@@ -505,13 +521,11 @@ mod tests {
 
     #[test]
     fn a_panic_inside_the_scope_still_removes_the_marker() {
-        let _turn = GLOBAL.lock().unwrap_or_else(|e| e.into_inner());
         let dir = std::env::temp_dir().join(format!("lc-gpu-panic-{}", std::process::id()));
         let m = dir.join("gpu-init.marker");
         let _ = std::fs::remove_dir_all(&dir);
-        set_init_marker(Some(m.clone()));
-        let r = std::panic::catch_unwind(|| with_marker("kernel compilation", || panic!("compile")));
-        set_init_marker(None);
+        let active = Mutex::new(0);
+        let r = std::panic::catch_unwind(|| with_marker_on(Some(m.clone()), &active, "kernel compilation", || panic!("compile")));
         assert!(r.is_err());
         assert!(!m.exists(), "the process survived, so nothing is left to report");
         let _ = std::fs::remove_dir_all(&dir);