diff --git a/testing/test_tmpdir.py b/testing/test_tmpdir.py
index 363172110d3..8d9d2777664 100644
--- a/testing/test_tmpdir.py
+++ b/testing/test_tmpdir.py
@@ -367,6 +367,21 @@ def test_get_user(monkeypatch):
     assert get_user() is None
 
 
+@pytest.mark.skipif(not sys.platform.startswith("win"), reason="win only")
+def test_get_user_handles_oserror(monkeypatch):
+    """Test that get_user() returns None when getpass.getuser() raises OSError.
+    
+    This handles the Python 3.13+ behavior where getpass.getuser() raises
+    OSError when no username environment variables (LOGNAME, USER, LNAME,
+    USERNAME) are set on Windows (#11874).
+    """
+    monkeypatch.delenv("LOGNAME", raising=False)
+    monkeypatch.delenv("USER", raising=False)
+    monkeypatch.delenv("LNAME", raising=False)
+    monkeypatch.delenv("USERNAME", raising=False)
+    assert get_user() is None
+
+
 class TestNumberedDir:
     PREFIX = "fun-"