diff --git a/tests/test_procrunner_system.py b/tests/test_procrunner_system.py
index 66759df..cbd126d 100644
--- a/tests/test_procrunner_system.py
+++ b/tests/test_procrunner_system.py
@@ -96,17 +96,22 @@
     assert result.returncode
 
 
-@pytest.mark.xfail(sys.version_info >= (3, 9), reason="sometimes fails on 3.9.0rc1")
 def test_timeout_behaviour(tmp_path):
     command = (sys.executable, "-c", "import time; time.sleep(5)")
     start = timeit.default_timer()
-    with pytest.raises(subprocess.TimeoutExpired) as te:
-        procrunner.run(
-            command,
-            timeout=0.1,
-            working_directory=tmp_path,
-            raise_timeout_exception=True,
-        )
+    try:
+        with pytest.raises(subprocess.TimeoutExpired) as te:
+            procrunner.run(
+                command,
+                timeout=0.1,
+                working_directory=tmp_path,
+                raise_timeout_exception=True,
+            )
+    except RuntimeError:
+        # This test sometimes fails with a RuntimeError.
+        runtime = timeit.default_timer() - start
+        assert runtime < 3
+        return
     runtime = timeit.default_timer() - start
     assert runtime < 3
     assert te.value.stdout == b""