diff --git a/exdir/core/exdir_file.py b/exdir/core/exdir_file.py
index ebca14c..4ba785c 100644
--- a/exdir/core/exdir_file.py
+++ b/exdir/core/exdir_file.py
@@ -115,14 +115,24 @@ def __init__(self, directory, mode=None, allow_remove=False,
         else:
             self.io_mode = OpenMode.READ_WRITE
 
+        parent_path = pathlib.PurePosixPath("")
         super().__init__(
             root_directory=directory,
-            parent_path=pathlib.PurePosixPath(""),
+            parent_path=parent_path,
             object_name="",
             file=self
         )
 
-        already_exists = directory.exists()
+        # If we have name validation, we need to check for uniqueness.  The
+        # directory may exist but with a different case, in which case we
+        # don't want to say that is already exists so that it matches the
+        # correct checks for the requested mode.
+        if name_validation != validation.none:
+            already_exists = validation.path_already_exists_case_insensitive(
+                directory.parent, directory.name.lower()
+            )
+        else:
+            already_exists = directory.exists()
         if already_exists:
             if not exob.is_nonraw_object_directory(directory):
                 raise RuntimeError(
diff --git a/exdir/core/validation.py b/exdir/core/validation.py
index 2b4b850..d47fa3f 100644
--- a/exdir/core/validation.py
+++ b/exdir/core/validation.py
@@ -1,7 +1,7 @@
 from enum import Enum
-import os
+import os.path
 import sys
-from pathlib import Path, WindowsPath
+from tempfile import NamedTemporaryFile
 from unicodedata import category
 from . import constants as exob
 
@@ -36,13 +36,14 @@ def _contains_control_character(s):
 
 def _assert_unique(parent_path, name):
     try:
-        name_str = str(name)
+        name = str(name)
     except UnicodeEncodeError:
         name = name.encode('utf8')
 
-    if (parent_path / name).exists():
+    if path_already_exists_case_insensitive(parent_path, name.lower()):
         raise RuntimeError(
-            "'{}' already exists in '{}'".format(name, parent_path)
+            "A directory with name (case independent) '{}' already exists "
+            " and cannot be made according to the naming rule 'thorough'.".format(name)
         )
 
 
@@ -108,6 +109,7 @@ def strict(parent_path, name):
     _assert_unique(parent_path, name)
     _assert_valid_characters(name)
 
+
 def thorough(parent_path, name):
     _assert_nonempty(parent_path, name)
     _assert_nonreserved(name)
@@ -117,21 +119,16 @@ def thorough(parent_path, name):
         name_str = name.encode('utf8')
     name_lower = name_str.lower()
     _assert_valid_characters(name_lower)
+    _assert_unique(parent_path, name)
+
+
+def none(parent_path, name):
+    pass
 
-    if isinstance(Path(parent_path), WindowsPath):
-        # use _assert_unique if we're already on Windows, because it is much faster
-        # than the test below
-        _assert_unique(parent_path, name)
-        return
 
+def path_already_exists_case_insensitive(parent_path, name_lower):
     # os.listdir is much faster here than os.walk or parent_path.iterdir
     for item in os.listdir(str(parent_path)):
         if name_lower == item.lower():
-            raise RuntimeError(
-                "A directory with name (case independent) '{}' already exists "
-                " and cannot be made according to the naming rule 'thorough'.".format(name)
-            )
-
-
-def none(parent_path, name):
-    pass
+            return True
+    return False
diff --git a/tests/test_file.py b/tests/test_file.py
index 12d80d6..82d2e92 100644
--- a/tests/test_file.py
+++ b/tests/test_file.py
@@ -187,6 +187,7 @@ def test_validate_name_thorough(setup_teardown_folder):
     f.close()
 
     with pytest.raises(RuntimeError):
+        # breakpoint()
         File(setup_teardown_folder[0] / "Test.exdir", name_validation=fv.thorough)
     with pytest.raises(NameError):
         File(setup_teardown_folder[0] / "tes#.exdir", name_validation=fv.thorough)