diff --git a/scrapy/extensions/httpcache.py b/scrapy/extensions/httpcache.py
index dd5bce24f..3f4af42b7 100644
--- a/scrapy/extensions/httpcache.py
+++ b/scrapy/extensions/httpcache.py
@@ -315,7 +315,9 @@ class FilesystemCacheStorage:
         self.expiration_secs: int = settings.getint("HTTPCACHE_EXPIRATION_SECS")
         self.use_gzip: bool = settings.getbool("HTTPCACHE_GZIP")
         # https://github.com/python/mypy/issues/10740
-        self._open: Callable[Concatenate[Union[str, os.PathLike], str, ...], IO] = (
+        self._open: Callable[
+            Concatenate[Union[str, os.PathLike], str, ...], IO[bytes]
+        ] = (
             gzip.open if self.use_gzip else open  # type: ignore[assignment]
         )
 
@@ -368,11 +370,12 @@ class FilesystemCacheStorage:
         with self._open(rpath / "pickled_meta", "wb") as f:
             pickle.dump(metadata, f, protocol=4)
         with self._open(rpath / "response_headers", "wb") as f:
-            f.write(headers_dict_to_raw(response.headers))
+            # headers_dict_to_raw() needs a better type hint
+            f.write(cast(bytes, headers_dict_to_raw(response.headers)))
         with self._open(rpath / "response_body", "wb") as f:
             f.write(response.body)
         with self._open(rpath / "request_headers", "wb") as f:
-            f.write(headers_dict_to_raw(request.headers))
+            f.write(cast(bytes, headers_dict_to_raw(request.headers)))
         with self._open(rpath / "request_body", "wb") as f:
             f.write(request.body)
 
diff --git a/scrapy/mail.py b/scrapy/mail.py
index fd6302550..f4ce2800c 100644
--- a/scrapy/mail.py
+++ b/scrapy/mail.py
@@ -97,7 +97,7 @@ class MailSender:
         subject: str,
         body: str,
         cc: Union[str, List[str], None] = None,
-        attachs: Sequence[Tuple[str, str, IO]] = (),
+        attachs: Sequence[Tuple[str, str, IO[Any]]] = (),
         mimetype: str = "text/plain",
         charset: Optional[str] = None,
         _callback: Optional[Callable[..., None]] = None,
@@ -214,7 +214,7 @@ class MailSender:
         return d
 
     def _create_sender_factory(
-        self, to_addrs: List[str], msg: IO, d: Deferred
+        self, to_addrs: List[str], msg: IO[bytes], d: Deferred
     ) -> ESMTPSenderFactory:
         from twisted.mail.smtp import ESMTPSenderFactory
 
diff --git a/scrapy/pipelines/files.py b/scrapy/pipelines/files.py
index 47457f2a8..c1ce0939c 100644
--- a/scrapy/pipelines/files.py
+++ b/scrapy/pipelines/files.py
@@ -47,7 +47,7 @@ def _to_string(path: Union[str, PathLike]) -> str:
     return str(path)  # convert a Path object to string
 
 
-def _md5sum(file: IO) -> str:
+def _md5sum(file: IO[bytes]) -> str:
     """Calculate the md5 checksum of a file-like object without reading its
     whole content in memory.
 
diff --git a/scrapy/utils/ftp.py b/scrapy/utils/ftp.py
index c77681a53..152f3374e 100644
--- a/scrapy/utils/ftp.py
+++ b/scrapy/utils/ftp.py
@@ -21,7 +21,7 @@ def ftp_makedirs_cwd(ftp: FTP, path: str, first_call: bool = True) -> None:
 def ftp_store_file(
     *,
     path: str,
-    file: IO,
+    file: IO[bytes],
     host: str,
     port: int,
     username: str,
diff --git a/scrapy/utils/misc.py b/scrapy/utils/misc.py
index faf52e44a..b678d1def 100644
--- a/scrapy/utils/misc.py
+++ b/scrapy/utils/misc.py
@@ -111,7 +111,7 @@ def walk_modules(path: str) -> List[ModuleType]:
     return mods
 
 
-def md5sum(file: IO) -> str:
+def md5sum(file: IO[bytes]) -> str:
     """Calculate the md5 checksum of a file-like object without reading its
     whole content in memory.