diff --git a/python/tests/test_util.py b/python/tests/test_util.py
index c99b5e2..9a21f46 100644
--- a/python/tests/test_util.py
+++ b/python/tests/test_util.py
@@ -83,11 +83,7 @@ def test_download_http_mirror(pyproject_toml: Path, server: Server) -> None:
 
 def test_download_file_mirror(pyproject_toml: Path, tmp_path: Path) -> None:
     mirror_dir = tmp_path / "mirror"
-    mirror_url = (
-        f"file:///{mirror_dir.as_posix()}"
-        if Platform.current().is_windows
-        else f"file://{mirror_dir}"
-    )
+    mirror_url = f"file:{'///' if Platform.current().is_windows else '//'}{mirror_dir}"
     pyproject_toml.write_text(
         dedent(
             f"""\