diff --git a/crates/engine/src/save_format_tests.rs b/crates/engine/src/save_format_tests.rs
index d635808e..fc4ca775 100644
--- a/crates/engine/src/save_format_tests.rs
+++ b/crates/engine/src/save_format_tests.rs
@@ -15,8 +15,12 @@ struct SaveFiles {
 
 impl SaveFiles {
     fn new() -> Self {
+        // Tests run in parallel and the clock can read the same for two of them (macOS counts
+        // microseconds), so a counter keeps their folders apart.
+        static NEXT: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
+        let n = NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
         let stamp = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap().as_nanos();
-        let dir = std::env::temp_dir().join(format!("figcraft-save-formats-{}-{stamp}", std::process::id()));
+        let dir = std::env::temp_dir().join(format!("figcraft-save-formats-{}-{stamp}-{n}", std::process::id()));
         std::fs::create_dir(&dir).unwrap();
         Self { dir, files: Vec::new() }
     }