diff --git a/pylsp/_utils.py b/pylsp/_utils.py
index c9eb6fb1..e9b5b4ff 100644
--- a/pylsp/_utils.py
+++ b/pylsp/_utils.py
@@ -96,7 +96,13 @@ def find_parents(root, path, names):
     # Split the relative by directory, generate all the parent directories, then check each of them.
     # This avoids running a loop that has different base-cases for unix/windows
     # e.g. /a/b and /a/b/c/d/e.py -> ['/a/b', 'c', 'd']
-    dirs = [root] + os.path.relpath(os.path.dirname(path), root).split(os.path.sep)
+    try:
+        dirs = [root] + os.path.relpath(os.path.dirname(path), root).split(os.path.sep)
+    except ValueError:
+        # On Windows, relpath raises ValueError when path and root are on different mounts
+        # (e.g. a UNC share root vs a drive-letter path). Nothing to find in this case.
+        log.warning("Path %r not in %r", path, root)
+        return []
 
     # Search each of /a/b/c, /a/b, /a
     while dirs:
diff --git a/test/test_utils.py b/test/test_utils.py
index 7ed6214f..e48449de 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -197,6 +197,19 @@ def test_find_parents(tmpdir) -> None:
     ]
 
 
+def test_find_parents_cross_mount(tmpdir, monkeypatch) -> None:
+    """find_parents returns [] when root and path are on different mounts (Windows UNC)."""
+    import unittest.mock as mock
+
+    subsubdir = tmpdir.ensure_dir("subdir", "subsubdir")
+    path = subsubdir.ensure("path.py")
+
+    with mock.patch("os.path.relpath", side_effect=ValueError("path is on mount 'C:', start on mount '\\\\unc\\share'")):
+        result = _utils.find_parents(tmpdir.strpath, path.strpath, ["test.cfg"])
+
+    assert result == []
+
+
 def test_merge_dicts() -> None:
     assert _utils.merge_dicts(
         {"a": True, "b": {"x": 123, "y": {"hello": "world"}}},