diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 778e2866f1eff..bdfb44cdc2fa3 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -50,7 +50,7 @@
     pandas_dtype,
 )
 from pandas.core.dtypes.concat import concat_categorical, concat_datetime
-from pandas.core.dtypes.dtypes import CategoricalDtype, ExtensionDtype
+from pandas.core.dtypes.dtypes import ExtensionDtype
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
     ABCExtensionArray,
@@ -183,21 +183,6 @@ def is_datelike(self) -> bool:
         """ return True if I am a non-datelike """
         return self.is_datetime or self.is_timedelta
 
-    def is_categorical_astype(self, dtype) -> bool:
-        """
-        validate that we have a astypeable to categorical,
-        returns a boolean if we are a categorical
-        """
-        if dtype is Categorical or dtype is CategoricalDtype:
-            # this is a pd.Categorical, but is not
-            # a valid type for astypeing
-            raise TypeError(f"invalid type {dtype} for astype")
-
-        elif is_categorical_dtype(dtype):
-            return True
-
-        return False
-
     def external_values(self):
         """
         The array that Series.values returns (public attribute).
@@ -565,7 +550,7 @@ def astype(self, dtype, copy: bool = False, errors: str = "raise"):
             raise TypeError(msg)
 
         # may need to convert to categorical
-        if self.is_categorical_astype(dtype):
+        if is_categorical_dtype(dtype):
 
             if is_categorical_dtype(self.values):
                 # GH 10696/18593: update an existing categorical efficiently
diff --git a/pandas/tests/series/test_dtypes.py b/pandas/tests/series/test_dtypes.py
index 31f17be2fac7b..2f2a663d559d0 100644
--- a/pandas/tests/series/test_dtypes.py
+++ b/pandas/tests/series/test_dtypes.py
@@ -311,9 +311,10 @@ def cmp(a, b):
 
         # invalid conversion (these are NOT a dtype)
         msg = (
-            r"invalid type <class 'pandas\.core\.arrays\.categorical\."
-            "Categorical'> for astype"
+            "dtype '<class 'pandas.core.arrays.categorical.Categorical'>' "
+            "not understood"
         )
+
         for invalid in [
             lambda x: x.astype(Categorical),
             lambda x: x.astype("object").astype(Categorical),