diff --git a/numcodecs/abc.py b/numcodecs/abc.py
index 5aba8c25..decd84ca 100644
--- a/numcodecs/abc.py
+++ b/numcodecs/abc.py
@@ -29,14 +29,13 @@
 """
 
 from abc import ABC, abstractmethod
-from typing import Optional
 
 
 class Codec(ABC):
     """Codec abstract base class."""
 
     # override in sub-class
-    codec_id: Optional[str] = None
+    codec_id: str | None = None
     """Codec identifier."""
 
     @abstractmethod
diff --git a/numcodecs/checksum32.py b/numcodecs/checksum32.py
index fc6cafd0..b7d5bf0b 100644
--- a/numcodecs/checksum32.py
+++ b/numcodecs/checksum32.py
@@ -3,7 +3,7 @@
 import zlib
 from contextlib import suppress
 from types import ModuleType
-from typing import Literal, Optional
+from typing import Literal
 
 import numpy as np
 from typing_extensions import Buffer
@@ -12,7 +12,7 @@
 from .compat import ensure_contiguous_ndarray, ndarray_copy
 from .jenkins import jenkins_lookup3
 
-_crc32c: Optional[ModuleType] = None
+_crc32c: ModuleType | None = None
 with suppress(ImportError):
     import crc32c as _crc32c  # type: ignore[no-redef, unused-ignore]
 
diff --git a/numcodecs/lzma.py b/numcodecs/lzma.py
index 5c1a57ca..7b6b2348 100644
--- a/numcodecs/lzma.py
+++ b/numcodecs/lzma.py
@@ -1,7 +1,6 @@
 from types import ModuleType
-from typing import Optional
 
-_lzma: Optional[ModuleType] = None
+_lzma: ModuleType | None = None
 try:
     import lzma as _lzma
 except ImportError:  # pragma: no cover
diff --git a/numcodecs/tests/test_zarr3.py b/numcodecs/tests/test_zarr3.py
index 8e2d1264..6102939e 100644
--- a/numcodecs/tests/test_zarr3.py
+++ b/numcodecs/tests/test_zarr3.py
@@ -122,8 +122,8 @@ def test_generic_filter(
             ],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic", mode="r")
     np.testing.assert_array_equal(data, a[:, :])
 
 
@@ -140,8 +140,8 @@ def test_generic_filter_bitround(store: StorePath):
             filters=[numcodecs.zarr3.BitRound(keepbits=3)],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic_bitround", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic_bitround", mode="r")
     assert np.allclose(data, a[:, :], atol=0.1)
 
 
@@ -158,8 +158,8 @@ def test_generic_filter_quantize(store: StorePath):
             filters=[numcodecs.zarr3.Quantize(digits=3)],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic_quantize", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic_quantize", mode="r")
     assert np.allclose(data, a[:, :], atol=0.001)
 
 
@@ -177,8 +177,8 @@ def test_generic_filter_packbits(store: StorePath):
             filters=[numcodecs.zarr3.PackBits()],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic_packbits", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic_packbits", mode="r")
     np.testing.assert_array_equal(data, a[:, :])
 
     with pytest.raises(ValueError, match=".*requires bool dtype.*"):
@@ -217,8 +217,8 @@ def test_generic_checksum(
             compressors=[codec_class()],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic_checksum", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic_checksum", mode="r")
     np.testing.assert_array_equal(data, a[:, :])
 
 
@@ -267,8 +267,8 @@ def test_delta_astype(store: StorePath):
             ],
         )
 
-        a[:, :] = data.copy()
-        a = zarr.open_array(store / "generic", mode="r")
+    a[:, :] = data.copy()
+    a = zarr.open_array(store / "generic", mode="r")
     np.testing.assert_array_equal(data, a[:, :])
 
 
diff --git a/numcodecs/zfpy.py b/numcodecs/zfpy.py
index 831952a5..80a1e78a 100644
--- a/numcodecs/zfpy.py
+++ b/numcodecs/zfpy.py
@@ -2,9 +2,8 @@
 from contextlib import suppress
 from importlib.metadata import PackageNotFoundError, version
 from types import ModuleType
-from typing import Optional
 
-_zfpy: Optional[ModuleType] = None
+_zfpy: ModuleType | None = None
 
 _zfpy_version: tuple = ()
 with suppress(PackageNotFoundError):