diff --git a/tests/conftest.py b/tests/conftest.py
index 28a7ef64..5d5ce803 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -124,8 +124,12 @@ def cpu_scaling_factor() -> float:
     # headroom. Apply a flat CI bump so every timing-test deadline
     # /assert that keys off this factor gets headroom on CI HW
     # (compounds with any local-throttle factor).
+    #
+    # macOS runners are noticeably slower + noisier than the linux
+    # ones for our multi-actor cancel-cascade tests, so give them
+    # extra headroom (3x vs 2x).
     if _ci_env:
-        factor *= 2
+        factor *= 3 if _non_linux else 2
 
     return factor
 
diff --git a/tests/test_cancellation.py b/tests/test_cancellation.py
index 371d70ad..5566691a 100644
--- a/tests/test_cancellation.py
+++ b/tests/test_cancellation.py
@@ -955,6 +955,12 @@ def test_fast_graceful_cancel_when_spawn_task_in_soft_proc_wait_for_daemon(
     if _friggin_windows:  # smh
         timeout += 1
 
+    # CPU-scaling / CI latency headroom — macOS CI especially is
+    # slow for this graceful-vs-hard-reap timing race; see
+    # `cpu_scaling_factor()`.
+    from .conftest import cpu_scaling_factor
+    timeout *= cpu_scaling_factor()
+
     async def main():
         start = time.time()
         try: