@@ -15,24 +15,19 @@
 
 # typing ------------------------------------------------------------------
 
-from typing import Any, Iterator, List, Match, Optional, Tuple, Type, Union, TYPE_CHECKING
-from git.types import PathLike, TBD, Literal, TypeGuard
+from typing import Any, Iterator, List, Match, Optional, Tuple, Type, Union, TYPE_CHECKING, cast
+from git.types import PathLike, TBD, Literal
 
 if TYPE_CHECKING:
     from .objects.tree import Tree
     from git.repo.base import Repo
 
     from subprocess import Popen
 
-Lit_change_type = Literal['A', 'C', 'D', 'M', 'R', 'T']
-
-
-def is_change_type(inp: str) -> TypeGuard[Lit_change_type]:
-    return inp in ('A', 'D', 'C', 'M', 'R', 'T')
+Lit_change_type = Literal['A', 'D', 'C', 'M', 'R', 'T']
 
 # ------------------------------------------------------------------------
 
-
 __all__ = ('Diffable', 'DiffIndex', 'Diff', 'NULL_TREE')
 
 # Special object to compare against the empty tree in diffs
@@ -205,8 +200,8 @@ def iter_change_type(self, change_type: Lit_change_type) -> Iterator['Diff']:
         if change_type not in self.change_type:
             raise ValueError("Invalid change type: %s" % change_type)
 
-        # diff: 'Diff'
         for diff in self:
+            diff = cast('Diff', diff)
             if diff.change_type == change_type:
                 yield diff
             elif change_type == "A" and diff.new_file:
@@ -287,8 +282,7 @@ def __init__(self, repo: 'Repo',
                  a_mode: Union[bytes, str, None], b_mode: Union[bytes, str, None],
                  new_file: bool, deleted_file: bool, copied_file: bool,
                  raw_rename_from: Optional[bytes], raw_rename_to: Optional[bytes],
-                 diff: Union[str, bytes, None], change_type: Union[Lit_change_type, None],
-                 score: Optional[int]) -> None:
+                 diff: Union[str, bytes, None], change_type: Optional[str], score: Optional[int]) -> None:
 
         assert a_rawpath is None or isinstance(a_rawpath, bytes)
         assert b_rawpath is None or isinstance(b_rawpath, bytes)
@@ -505,15 +499,13 @@ def _handle_diff_line(lines_bytes: bytes, repo: 'Repo', index: DiffIndex) -> Non
         for line in lines.split(':')[1:]:
             meta, _, path = line.partition('\x00')
             path = path.rstrip('\x00')
-            a_blob_id: Union[str, None]
-            b_blob_id: Union[str, None]
+            a_blob_id: Optional[str]
+            b_blob_id: Optional[str]
             old_mode, new_mode, a_blob_id, b_blob_id, _change_type = meta.split(None, 4)
-            # _Change_type can be R100
+            # Change type can be R100
             # R: status letter
             # 100: score (in case of copy and rename)
-
-            assert is_change_type(_change_type[0]), "Unexpected _change_type recieved in Diff"
-            change_type: Lit_change_type = _change_type[0]
+            change_type: Lit_change_type = _change_type[0]  # type: ignore
             score_str = ''.join(_change_type[1:])
             score = int(score_str) if score_str.isdigit() else None
             path = path.strip()
@@ -528,7 +520,7 @@ def _handle_diff_line(lines_bytes: bytes, repo: 'Repo', index: DiffIndex) -> Non
             # NOTE: We cannot conclude from the existence of a blob to change type
             # as diffs with the working do not have blobs yet
             if change_type == 'D':
-                b_blob_id = None
+                b_blob_id = None  # Optional[str]
                 deleted_file = True
             elif change_type == 'A':
                 a_blob_id = None
 
@@ -391,7 +391,7 @@ def add(cls, repo: 'Repo', name: str, path: PathLike, url: Union[str, None] = No
         if sm.exists():
             # reretrieve submodule from tree
             try:
-                sm = repo.head.commit.tree[path]  # type: ignore
+                sm = repo.head.commit.tree[path]   # type: ignore
                 sm._name = name
                 return sm
             except KeyError: