diff --git a/Modules/Core/Common/wrapping/test/itkPointSetSerializationTest.py b/Modules/Core/Common/wrapping/test/itkPointSetSerializationTest.py
index 6bfaac2d562..ef79172e563 100644
--- a/Modules/Core/Common/wrapping/test/itkPointSetSerializationTest.py
+++ b/Modules/Core/Common/wrapping/test/itkPointSetSerializationTest.py
@@ -48,10 +48,7 @@ def test_point_set_serialization(use_unsafe_SetPoints_overload: bool = False):
 
     # Set Points in the PointSet
     PointType = itk.Point[itk.F, 3]
-    if os.name == "nt":
-        v_point = itk.VectorContainer[itk.ULL, PointType].New()
-    else:
-        v_point = itk.VectorContainer[itk.UL, PointType].New()
+    v_point = itk.VectorContainer[itk.uint64_t, PointType].New()
     v_point.Reserve(NumberOfPoints)
 
     point = PointType()
diff --git a/Modules/Core/Mesh/wrapping/test/itkMeshSerializationTest.py b/Modules/Core/Mesh/wrapping/test/itkMeshSerializationTest.py
index 9c39b434d36..59ac109a32c 100644
--- a/Modules/Core/Mesh/wrapping/test/itkMeshSerializationTest.py
+++ b/Modules/Core/Mesh/wrapping/test/itkMeshSerializationTest.py
@@ -45,10 +45,7 @@ def test_mesh_serialization(use_unsafe_SetPoints_overload: bool = False):
 
     # Set Points in the Mesh
     PointType = itk.Point[itk.F, 3]
-    if os.name == "nt":
-        v_point = itk.VectorContainer[itk.ULL, PointType].New()
-    else:
-        v_point = itk.VectorContainer[itk.UL, PointType].New()
+    v_point = itk.VectorContainer[itk.uint64_t, PointType].New()
     v_point.Reserve(NumberOfPoints)
 
     point = PointType()
diff --git a/Wrapping/Generators/Python/itk/support/extras.py b/Wrapping/Generators/Python/itk/support/extras.py
index 5c9f16704f1..24a1653dadd 100644
--- a/Wrapping/Generators/Python/itk/support/extras.py
+++ b/Wrapping/Generators/Python/itk/support/extras.py
@@ -268,18 +268,12 @@ def _get_itk_pixelid(numpy_array_type):
 
     import itk
 
-    def _long_type():
-        if os.name == "nt":
-            return itk.ULL
-        else:
-            return itk.UL
-
     # This is a Mapping from numpy array types to itk pixel types.
     _np_itk = {
         np.dtype(np.uint8): itk.UC,
         np.dtype(np.uint16): itk.US,
         np.dtype(np.uint32): itk.UI,
-        np.dtype(np.uint64): _long_type(),
+        np.dtype(np.uint64): itk.uint64_t,
         np.dtype(np.int8): itk.SC,
         np.dtype(np.int16): itk.SS,
         np.dtype(np.int32): itk.SI,
@@ -551,10 +545,7 @@ def vector_container_from_array(arr: ArrayLike, ttype=None) -> itkt.VectorContai
         arr = np.asarray(arr)
 
     # Return VectorContainer with 64-bit index type
-    if os.name == "nt":
-        IndexType = itk.ULL
-    else:
-        IndexType = itk.UL
+    IndexType = itk.uint64_t
 
     # Find container type
     if ttype is not None:
@@ -907,10 +898,7 @@ def dict_from_mesh(mesh: itkt.Mesh) -> dict:
     else:
         cell_data_numpy = itk.array_from_vector_container(cell_data)
 
-    if os.name == "nt":
-        cell_component_type = python_to_js(itk.ULL)
-    else:
-        cell_component_type = python_to_js(itk.UL)
+    cell_component_type = python_to_js(itk.uint64_t)
 
     point_component_type = python_to_js(itk.F)
 
@@ -982,10 +970,7 @@ def dict_from_pointset(pointset: itkt.PointSet) -> dict:
     else:
         point_data_numpy = itk.array_from_vector_container(point_data)
 
-    if os.name == "nt":
-        cell_component_type = python_to_js(itk.ULL)
-    else:
-        cell_component_type = python_to_js(itk.UL)
+    cell_component_type = python_to_js(itk.uint64_t)
 
     point_component_type = python_to_js(itk.F)
 
diff --git a/Wrapping/Generators/Python/itk/support/types.py b/Wrapping/Generators/Python/itk/support/types.py
index 759c3a2571a..9eb29cfc1b9 100644
--- a/Wrapping/Generators/Python/itk/support/types.py
+++ b/Wrapping/Generators/Python/itk/support/types.py
@@ -158,13 +158,9 @@ def initialize_c_types_once(cls) -> tuple[Self, ...]:
 int64_t = SL if SL.dtype.itemsize == 8 else SLL
 
 # Aliases for SizeValueType, IdentifierType, OffsetType
-ST = UL
-IT = UL
-OT = SL
-if os.name == "nt":
-    ST = ULL
-    IT = ULL
-    OT = SLL
+ST = uint64_t
+IT = uint64_t
+OT = int64_t
 
 # Type aliases to avoid expensive import, circular references. Use with forward references.
 if TYPE_CHECKING: