diff --git a/backend/tests/test_plex_subtitle_prepare.py b/backend/tests/test_plex_subtitle_prepare.py
index 53085c17..fcaa4aa0 100644
--- a/backend/tests/test_plex_subtitle_prepare.py
+++ b/backend/tests/test_plex_subtitle_prepare.py
@@ -22,6 +22,7 @@ conftest refuses to run without ffmpeg rather than let it skip.
 """
 
 import asyncio
+import errno
 import shutil
 import subprocess
 import sys
@@ -1059,7 +1060,17 @@ def test_an_absurd_rating_key_or_ordinal_is_refused_not_a_500(client, monkeypatc
     ):
         assert client.get(url).status_code == 422, url
     assert pool.jobs == []
-    # …and the cache helpers themselves no longer throw on such a name.
+
+    # …and the cache helpers themselves no longer throw on such a name. Asserted against a forced
+    # ENAMETOOLONG rather than the real filesystem: on Linux pathlib re-raises it (the defect), but
+    # Windows reports ERROR_INVALID_NAME, which pathlib's `exists()` already swallows — so on a dev
+    # machine this assertion passed with `_exists` reverted and only the container lane was honest
+    # about it (deep-review round 5).
+    def _too_long(self):
+        raise OSError(errno.ENAMETOOLONG, "File name too long")
+
+    monkeypatch.setattr(Path, "exists", _too_long)
+    assert subtitles._exists(Path("whatever")) is False
     assert subtitles.read_meta(subtitles.cache_key(long_key, 0)) == ([], False)