diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
index 3915296ef..003ed92c1 100644
--- a/.github/workflows/pythonpackage.yml
+++ b/.github/workflows/pythonpackage.yml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: ["ubuntu-latest", "windows-latest"]
+        os: ["ubuntu-latest", "macos-13", "windows-latest"]
         python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
         include:
         - experimental: false
diff --git a/test/test_util.py b/test/test_util.py
index f1ce17bca..428bd07c3 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -398,7 +398,9 @@ def test_blocking_lock_file(self):
         elapsed = time.time() - start
         extra_time = 0.02
         if os.name == "nt" or sys.platform == "cygwin":
-            extra_time *= 6  # NOTE: Indeterministic failures without this...
+            extra_time *= 6  # Without this, we get indeterministic failures on Windows.
+        elif sys.platform == "darwin":
+            extra_time *= 9  # The situation on macOS is similar, but with more delay.
         self.assertLess(elapsed, wait_time + extra_time)
 
     def test_user_id(self):