diff --git a/constraints-oldest.txt b/constraints-oldest.txt
index 1b729c34a..624813769 100644
--- a/constraints-oldest.txt
+++ b/constraints-oldest.txt
@@ -4,7 +4,7 @@
 # interpreter and Python ependencies. Keep this up-to-date with minimum
 # versions in `setup.cfg`.
 black==22.3.0
-darkgraylib==1.3.1
+darkgraylib==1.3.2
 defusedxml==0.7.1
 flake8-2020==1.6.1
 flake8-bugbear==22.1.11
diff --git a/setup.cfg b/setup.cfg
index 7c949e7cb..49f5bc70a 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -29,7 +29,7 @@ packages = find:
 install_requires =
     # NOTE: remember to keep `constraints-oldest.txt` in sync with these
     black>=22.3.0
-    darkgraylib~=1.3.1
+    darkgraylib~=1.3.2
     graylint~=1.1.2
     toml>=0.10.0
 # NOTE: remember to keep `.github/workflows/python-package.yml` in sync
diff --git a/src/darker/diff.py b/src/darker/diff.py
index 83e7d9abd..c53012a77 100644
--- a/src/darker/diff.py
+++ b/src/darker/diff.py
@@ -65,7 +65,7 @@
 """
 
 import logging
-from typing import Generator, List, Sequence, Tuple
+from typing import Generator, List, Literal, Sequence, Tuple
 
 from darker.multiline_strings import find_overlap
 from darkgraylib.diff import diff_and_get_opcodes, validate_opcodes
@@ -75,7 +75,9 @@
 
 
 def opcodes_to_edit_linenums(  # pylint: disable=too-many-locals
-    opcodes: List[Tuple[str, int, int, int, int]],
+    opcodes: List[
+        Tuple[Literal["replace", "delete", "insert", "equal"], int, int, int, int]
+    ],
     context_lines: int,
     multiline_string_ranges: Sequence[Tuple[int, int]],
 ) -> Generator[int, None, None]:
@@ -123,7 +125,9 @@ def opcodes_to_edit_linenums(  # pylint: disable=too-many-locals
 
 
 def opcodes_to_chunks(
-    opcodes: List[Tuple[str, int, int, int, int]],
+    opcodes: List[
+        Tuple[Literal["replace", "delete", "insert", "equal"], int, int, int, int]
+    ],
     src: TextDocument,
     dst: TextDocument,
 ) -> Generator[DiffChunk, None, None]:
diff --git a/src/darker/tests/test_diff.py b/src/darker/tests/test_diff.py
index ffdb1bb8e..6ab83b847 100644
--- a/src/darker/tests/test_diff.py
+++ b/src/darker/tests/test_diff.py
@@ -3,13 +3,11 @@
 # pylint: disable=use-dict-literal
 
 from itertools import chain
+from typing import List, Literal, Tuple
 
 import pytest
 
-from darker.diff import (
-    opcodes_to_chunks,
-    opcodes_to_edit_linenums,
-)
+from darker.diff import opcodes_to_chunks, opcodes_to_edit_linenums
 from darkgraylib.testtools.diff_helpers import (
     EXPECT_OPCODES,
     FUNCTIONS2_PY,
@@ -98,7 +96,9 @@ def test_opcodes_to_chunks():
     ]
 
 
-EXAMPLE_OPCODES = [
+EXAMPLE_OPCODES: List[
+    Tuple[Literal["replace", "delete", "insert", "equal"], int, int, int, int]
+] = [
     # 0-based, end-exclusive
     ("replace", 0, 4, 0, 1),
     ("equal", 4, 6, 1, 3),