diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 769ae52744c74..1398db6960cc8 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -49,6 +49,7 @@
 from pandas.core.dtypes.common import (
     ensure_int64,
     ensure_object,
+    ensure_platform_int,
     is_categorical_dtype,
     is_datetime64_dtype,
     is_dict_like,
@@ -533,7 +534,7 @@ def astype(self, dtype: Dtype, copy: bool = True) -> ArrayLike:
             # error: Incompatible types in assignment (expression has type "ndarray",
             # variable has type "Categorical")
             result = take_nd(  # type: ignore[assignment]
-                new_cats, libalgos.ensure_platform_int(self._codes)
+                new_cats, ensure_platform_int(self._codes)
             )
 
         return result
diff --git a/pandas/tests/apply/test_frame_transform.py b/pandas/tests/apply/test_frame_transform.py
index 1a12cbff47092..7a626ce6312c5 100644
--- a/pandas/tests/apply/test_frame_transform.py
+++ b/pandas/tests/apply/test_frame_transform.py
@@ -162,8 +162,6 @@ def test_transform_method_name(method):
 frame_kernels_raise = [x for x in frame_transform_kernels if x not in wont_fail]
 
 
-# mypy doesn't allow adding lists of different types
-# https://github.com/python/mypy/issues/5492
 @pytest.mark.parametrize("op", [*frame_kernels_raise, lambda x: x + 1])
 def test_transform_bad_dtype(op, frame_or_series):
     # GH 35964