From fd82e37d404a2d8150ffe346343f17b4ff223487 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Randy=20D=C3=B6ring?=
 <30527984+radoering@users.noreply.github.com>
Date: Fri, 20 Mar 2026 14:01:33 +0100
Subject: [PATCH 1/2] fix: handle special uint32 arrays on Windows correctly

---
 src/zarr/core/dtype/npy/int.py        | 22 ++++++++++++++++++++++
 tests/test_dtype/test_npy/test_int.py | 11 ++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/zarr/core/dtype/npy/int.py b/src/zarr/core/dtype/npy/int.py
index f71f535abb..e5007b7acb 100644
--- a/src/zarr/core/dtype/npy/int.py
+++ b/src/zarr/core/dtype/npy/int.py
@@ -1070,6 +1070,28 @@ class UInt32(BaseInt[np.dtypes.UInt32DType, np.uint32], HasEndianness):
     _zarr_v3_name: ClassVar[Literal["uint32"]] = "uint32"
     _zarr_v2_names: ClassVar[tuple[Literal[">u4"], Literal["<u4"]]] = (">u4", "<u4")
 
+    @classmethod
+    def _check_native_dtype(cls: type[Self], dtype: TBaseDType) -> TypeGuard[np.dtypes.UInt32DType]:
+        """
+        A type guard that checks if the input is assignable to the type of ``cls.dtype_class``
+
+        This method is overridden for this particular data type because of a Windows-specific issue
+        where ``np.array([1], dtype=np.uint32) & 1`` creates an instance of ``np.dtypes.UIntDType``,
+        rather than an instance of ``np.dtypes.UInt32DType``, even though both represent 32-bit
+        unsigned integers. (In contrast to ``np.dtype('i')``, ``np.dtype('u')`` raises an error.)
+
+        Parameters
+        ----------
+        dtype : TDType
+            The dtype to check.
+
+        Returns
+        -------
+        Bool
+            True if the dtype matches, False otherwise.
+        """
+        return super()._check_native_dtype(dtype) or dtype == np.dtypes.UInt32DType()
+
     @classmethod
     def from_native_dtype(cls, dtype: TBaseDType) -> Self:
         """
diff --git a/tests/test_dtype/test_npy/test_int.py b/tests/test_dtype/test_npy/test_int.py
index f53ec7f5ae..9eab053080 100644
--- a/tests/test_dtype/test_npy/test_int.py
+++ b/tests/test_dtype/test_npy/test_int.py
@@ -216,7 +216,16 @@ class TestUInt16(BaseTestZDType):
 class TestUInt32(BaseTestZDType):
     test_cls = UInt32
     scalar_type = np.uint32
-    valid_dtype = (np.dtype(">u4"), np.dtype("<u4"))
+
+    # On Windows, this creates an UIntDType (instead of UInt32DType),
+    # similar to how np.dtype('i') creates an IntDType instead of Int32DType.
+    # However, np.dtype('u') raises a TypeError.
+    uint_dtype = (np.array([1], dtype=np.uint32) & 1).dtype
+
+    # The behavior of some tests associated with this class variable are
+    # order-dependent -- uint_dtype correctly fails certain tests only if it's not
+    # in the last position of the tuple. I have no idea how this is possible!
+    valid_dtype = (uint_dtype, np.dtype(">u4"), np.dtype("<u4"))
     invalid_dtype = (
         np.dtype(np.int8),
         np.dtype(np.int16),

From 601d92b3b74c35ff7edef29fdbb5ad4835a9b5a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Randy=20D=C3=B6ring?=
 <30527984+radoering@users.noreply.github.com>
Date: Fri, 20 Mar 2026 14:10:05 +0100
Subject: [PATCH 2/2] add changelog entry

---
 changes/3797.bugfix.md | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 changes/3797.bugfix.md

diff --git a/changes/3797.bugfix.md b/changes/3797.bugfix.md
new file mode 100644
index 0000000000..c683213c5d
--- /dev/null
+++ b/changes/3797.bugfix.md
@@ -0,0 +1,2 @@
+Fix an issue that prevents the correct parsing of special NumPy ``uint32`` dtypes resulting e.g.
+from bit wise operations on ``uint32`` arrays on Windows.