diff --git a/pyproject.toml b/pyproject.toml
index ebfbede8559..d7f29ff1f09 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -118,7 +118,7 @@ sources = ["src"]
 enable-by-default = false
 dependencies = [
   "hatch-mypyc>=0.16.0",
-  "mypy==1.5.1",
+  "mypy==1.4.0",
   "click==8.1.3",  # avoid https://github.com/pallets/click/issues/2558
 ]
 require-runtime-dependencies = true
diff --git a/src/black/cache.py b/src/black/cache.py
index cbf63e2359d..ff15da2a94e 100644
--- a/src/black/cache.py
+++ b/src/black/cache.py
@@ -8,7 +8,6 @@
 from pathlib import Path
 from typing import Dict, Iterable, NamedTuple, Set, Tuple
 
-from mypy_extensions import mypyc_attr
 from platformdirs import user_cache_dir
 
 from _black_version import version as __version__
@@ -20,7 +19,6 @@
     from typing_extensions import Self
 
 
-@mypyc_attr(serializable=True)
 class FileData(NamedTuple):
     st_mtime: float
     st_size: int