diff --git a/openslide/__init__.py b/openslide/__init__.py
index 53c70756..65022b41 100644
--- a/openslide/__init__.py
+++ b/openslide/__init__.py
@@ -26,7 +26,6 @@
 from __future__ import annotations
 
 from io import BytesIO
-from pathlib import Path
 from types import TracebackType
 from typing import Iterator, Literal, Mapping, TypeVar
 
@@ -82,7 +81,7 @@ def __exit__(
         return False
 
     @classmethod
-    def detect_format(cls, filename: str | Path) -> str | None:
+    def detect_format(cls, filename: lowlevel.Filename) -> str | None:
         """Return a string describing the format of the specified file.
 
         If the file format is not recognized, return None."""
@@ -189,11 +188,11 @@ class OpenSlide(AbstractSlide):
     operations on the OpenSlide object, other than close(), will fail.
     """
 
-    def __init__(self, filename: str | Path):
+    def __init__(self, filename: lowlevel.Filename):
         """Open a whole-slide image."""
         AbstractSlide.__init__(self)
         self._filename = filename
-        self._osr = lowlevel.open(str(filename))
+        self._osr = lowlevel.open(filename)
         if lowlevel.read_icc_profile.available:
             self._profile = lowlevel.read_icc_profile(self._osr)
 
@@ -201,11 +200,11 @@ def __repr__(self) -> str:
         return f'{self.__class__.__name__}({self._filename!r})'
 
     @classmethod
-    def detect_format(cls, filename: str | Path) -> str | None:
+    def detect_format(cls, filename: lowlevel.Filename) -> str | None:
         """Return a string describing the format vendor of the specified file.
 
         If the file format is not recognized, return None."""
-        return lowlevel.detect_vendor(str(filename))
+        return lowlevel.detect_vendor(filename)
 
     def close(self) -> None:
         """Close the OpenSlide object."""
@@ -358,7 +357,7 @@ def __repr__(self) -> str:
 class ImageSlide(AbstractSlide):
     """A wrapper for a PIL.Image that provides the OpenSlide interface."""
 
-    def __init__(self, file: str | Path | Image.Image):
+    def __init__(self, file: lowlevel.Filename | Image.Image):
         """Open an image file.
 
         file can be a filename or a PIL.Image."""
@@ -376,7 +375,7 @@ def __repr__(self) -> str:
         return f'{self.__class__.__name__}({self._file_arg!r})'
 
     @classmethod
-    def detect_format(cls, filename: str | Path) -> str | None:
+    def detect_format(cls, filename: lowlevel.Filename) -> str | None:
         """Return a string describing the format of the specified file.
 
         If the file format is not recognized, return None."""
@@ -484,7 +483,7 @@ def set_cache(self, cache: OpenSlideCache) -> None:
         pass
 
 
-def open_slide(filename: str | Path) -> OpenSlide | ImageSlide:
+def open_slide(filename: lowlevel.Filename) -> OpenSlide | ImageSlide:
     """Open a whole-slide or regular image.
 
     Return an OpenSlide object for whole-slide images and an ImageSlide
diff --git a/openslide/lowlevel.py b/openslide/lowlevel.py
index 2042a9a5..159f91e1 100644
--- a/openslide/lowlevel.py
+++ b/openslide/lowlevel.py
@@ -2,7 +2,7 @@
 # openslide-python - Python bindings for the OpenSlide library
 #
 # Copyright (c) 2010-2013 Carnegie Mellon University
-# Copyright (c) 2016-2023 Benjamin Gilbert
+# Copyright (c) 2016-2024 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -48,6 +48,7 @@
     cdll,
 )
 from itertools import count
+import os
 import platform
 from typing import TYPE_CHECKING, Any, Callable, Protocol, TypeVar, cast
 
@@ -56,7 +57,7 @@
 from . import _convert
 
 if TYPE_CHECKING:
-    # Python 3.10+ for ParamSpec
+    # Python 3.10+
     from typing import ParamSpec, TypeAlias
 
     from _convert import _Buffer
@@ -196,6 +197,28 @@ def from_param(cls, obj: _OpenSlideCache) -> _OpenSlideCache:
         return obj
 
 
+if TYPE_CHECKING:
+    # Python 3.10+
+    Filename: TypeAlias = str | bytes | os.PathLike[Any]
+
+
+class _filename_p:
+    """Wrapper class to convert filename arguments to bytes."""
+
+    @classmethod
+    def from_param(cls, obj: Filename) -> bytes:
+        # fspath and fsencode throw TypeError on unexpected types
+        if platform.system() == 'Windows':
+            # OpenSlide 4.0.0+ requires UTF-8 on Windows
+            obj = os.fspath(obj)
+            if isinstance(obj, str):
+                return obj.encode('UTF-8')
+            else:
+                return obj
+        else:
+            return os.fsencode(obj)
+
+
 class _utf8_p:
     """Wrapper class to convert string arguments to bytes."""
 
@@ -350,14 +373,14 @@ def decorator(fn: Callable[_P, _T]) -> _Func[_P, _T]:
 
 
 try:
-    detect_vendor: _Func[[str], str] = _func(
-        'openslide_detect_vendor', c_char_p, [_utf8_p], _check_string
+    detect_vendor: _Func[[Filename], str] = _func(
+        'openslide_detect_vendor', c_char_p, [_filename_p], _check_string
     )
 except AttributeError:
     raise OpenSlideVersionError('3.4.0')
 
-open: _Func[[str], _OpenSlide] = _func(
-    'openslide_open', c_void_p, [_utf8_p], _check_open
+open: _Func[[Filename], _OpenSlide] = _func(
+    'openslide_open', c_void_p, [_filename_p], _check_open
 )
 
 close: _Func[[_OpenSlide], None] = _func(
diff --git "a/tests/fixtures/\360\237\230\220.png" "b/tests/fixtures/\360\237\230\220.png"
new file mode 100644
index 00000000..fccc4fe5
Binary files /dev/null and "b/tests/fixtures/\360\237\230\220.png" differ
diff --git "a/tests/fixtures/\360\237\230\220.svs" "b/tests/fixtures/\360\237\230\220.svs"
new file mode 100644
index 00000000..6d113e1d
Binary files /dev/null and "b/tests/fixtures/\360\237\230\220.svs" differ
diff --git a/tests/test_base.py b/tests/test_base.py
index bcced6f8..d03ce7cf 100644
--- a/tests/test_base.py
+++ b/tests/test_base.py
@@ -45,7 +45,7 @@ def test_lowlevel_available(self):
             if getattr(attr, '__module__', None) == '__future__':
                 continue
             # ignore random imports
-            if hasattr(ctypes, name) or name in ('count', 'platform'):
+            if hasattr(ctypes, name) or name in ('count', 'os', 'platform'):
                 continue
             self.assertTrue(
                 hasattr(attr, 'available'),
diff --git a/tests/test_imageslide.py b/tests/test_imageslide.py
index dd00ad66..e577851f 100644
--- a/tests/test_imageslide.py
+++ b/tests/test_imageslide.py
@@ -1,7 +1,7 @@
 #
 # openslide-python - Python bindings for the OpenSlide library
 #
-# Copyright (c) 2016-2023 Benjamin Gilbert
+# Copyright (c) 2016-2024 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -19,6 +19,7 @@
 
 from __future__ import annotations
 
+import sys
 import unittest
 
 from PIL import Image
@@ -44,6 +45,21 @@ def test_open_image(self):
                 self.assertEqual(osr.dimensions, (300, 250))
                 self.assertEqual(repr(osr), 'ImageSlide(%r)' % img)
 
+    @unittest.skipUnless(
+        sys.getfilesystemencoding() == 'utf-8',
+        'Python filesystem encoding is not UTF-8',
+    )
+    def test_unicode_path(self):
+        path = file_path('😐.png')
+        for arg in path, str(path):
+            self.assertEqual(ImageSlide.detect_format(arg), 'PNG')
+            self.assertEqual(ImageSlide(arg).dimensions, (300, 250))
+
+    def test_unicode_path_bytes(self):
+        arg = str(file_path('😐.png')).encode('UTF-8')
+        self.assertEqual(ImageSlide.detect_format(arg), 'PNG')
+        self.assertEqual(ImageSlide(arg).dimensions, (300, 250))
+
     def test_operations_on_closed_handle(self):
         with Image.open(file_path('boxes.png')) as img:
             osr = ImageSlide(img)
diff --git a/tests/test_openslide.py b/tests/test_openslide.py
index 7ee86363..b2257e58 100644
--- a/tests/test_openslide.py
+++ b/tests/test_openslide.py
@@ -1,7 +1,7 @@
 #
 # openslide-python - Python bindings for the OpenSlide library
 #
-# Copyright (c) 2016-2023 Benjamin Gilbert
+# Copyright (c) 2016-2024 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -61,12 +61,27 @@ def test_open(self):
         self.assertRaises(
             OpenSlideUnsupportedFormatError, lambda: OpenSlide('setup.py')
         )
-        self.assertRaises(OpenSlideUnsupportedFormatError, lambda: OpenSlide(None))
-        self.assertRaises(OpenSlideUnsupportedFormatError, lambda: OpenSlide(3))
+        self.assertRaises(ArgumentError, lambda: OpenSlide(None))
+        self.assertRaises(ArgumentError, lambda: OpenSlide(3))
         self.assertRaises(
             OpenSlideUnsupportedFormatError, lambda: OpenSlide('unopenable.tiff')
         )
 
+    @unittest.skipUnless(
+        sys.getfilesystemencoding() == 'utf-8',
+        'Python filesystem encoding is not UTF-8',
+    )
+    def test_unicode_path(self):
+        path = file_path('😐.svs')
+        for arg in path, str(path):
+            self.assertEqual(OpenSlide.detect_format(arg), 'aperio')
+            self.assertEqual(OpenSlide(arg).dimensions, (16, 16))
+
+    def test_unicode_path_bytes(self):
+        arg = str(file_path('😐.svs')).encode('UTF-8')
+        self.assertEqual(OpenSlide.detect_format(arg), 'aperio')
+        self.assertEqual(OpenSlide(arg).dimensions, (16, 16))
+
     def test_operations_on_closed_handle(self):
         osr = OpenSlide(file_path('boxes.tiff'))
         props = osr.properties