diff --git a/stdlib/os/__init__.pyi b/stdlib/os/__init__.pyi
index 6f51d4e7aa50..590d20576665 100644
--- a/stdlib/os/__init__.pyi
+++ b/stdlib/os/__init__.pyi
@@ -503,11 +503,14 @@ if sys.platform != "win32":
     def getenvb(key: bytes) -> bytes | None: ...
     @overload
     def getenvb(key: bytes, default: _T) -> bytes | _T: ...
+    def putenv(__name: StrOrBytesPath, __value: StrOrBytesPath) -> None: ...
+    def unsetenv(__name: StrOrBytesPath) -> None: ...
 
-def putenv(__name: bytes | str, __value: bytes | str) -> None: ...
+else:
+    def putenv(__name: str, __value: str) -> None: ...
 
-if sys.platform != "win32" or sys.version_info >= (3, 9):
-    def unsetenv(__name: bytes | str) -> None: ...
+    if sys.version_info >= (3, 9):
+        def unsetenv(__name: str) -> None: ...
 
 _Opener: TypeAlias = Callable[[str, int], int]
 
@@ -622,7 +625,7 @@ if sys.platform != "win32":
         def posix_fadvise(__fd: int, __offset: int, __length: int, __advice: int) -> None: ...
 
     def pread(__fd: int, __length: int, __offset: int) -> bytes: ...
-    def pwrite(__fd: int, __buffer: bytes, __offset: int) -> int: ...
+    def pwrite(__fd: int, __buffer: ReadableBuffer, __offset: int) -> int: ...
     # In CI, stubtest sometimes reports that these are available on MacOS, sometimes not
     def preadv(__fd: int, __buffers: SupportsLenAndGetItem[WriteableBuffer], __offset: int, __flags: int = ...) -> int: ...
     def pwritev(__fd: int, __buffers: SupportsLenAndGetItem[ReadableBuffer], __offset: int, __flags: int = ...) -> int: ...
@@ -641,8 +644,8 @@ if sys.platform != "win32":
         in_fd: int,
         offset: int,
         count: int,
-        headers: Sequence[bytes] = ...,
-        trailers: Sequence[bytes] = ...,
+        headers: Sequence[ReadableBuffer] = ...,
+        trailers: Sequence[ReadableBuffer] = ...,
         flags: int = ...,
     ) -> int: ...  # FreeBSD and Mac OS X only
     def readv(__fd: int, __buffers: SupportsLenAndGetItem[WriteableBuffer]) -> int: ...
@@ -671,7 +674,7 @@ if sys.platform != "win32":
     def tcsetpgrp(__fd: int, __pgid: int) -> None: ...
     def ttyname(__fd: int) -> str: ...
 
-def write(__fd: int, __data: bytes) -> int: ...
+def write(__fd: int, __data: ReadableBuffer) -> int: ...
 def access(
     path: _FdOrAnyPath, mode: int, *, dir_fd: int | None = ..., effective_ids: bool = ..., follow_symlinks: bool = ...
 ) -> bool: ...
@@ -775,14 +778,19 @@ if sys.platform != "win32":
     ) -> Iterator[tuple[str, list[str], list[str], int]]: ...
     @overload
     def fwalk(
-        top: bytes, topdown: bool = ..., onerror: _OnError | None = ..., *, follow_symlinks: bool = ..., dir_fd: int | None = ...
+        top: BytesPath,
+        topdown: bool = ...,
+        onerror: _OnError | None = ...,
+        *,
+        follow_symlinks: bool = ...,
+        dir_fd: int | None = ...,
     ) -> Iterator[tuple[bytes, list[bytes], list[bytes], int]]: ...
     if sys.platform == "linux":
         def getxattr(path: _FdOrAnyPath, attribute: StrOrBytesPath, *, follow_symlinks: bool = ...) -> bytes: ...
         def listxattr(path: _FdOrAnyPath | None = ..., *, follow_symlinks: bool = ...) -> list[str]: ...
         def removexattr(path: _FdOrAnyPath, attribute: StrOrBytesPath, *, follow_symlinks: bool = ...) -> None: ...
         def setxattr(
-            path: _FdOrAnyPath, attribute: StrOrBytesPath, value: bytes, flags: int = ..., *, follow_symlinks: bool = ...
+            path: _FdOrAnyPath, attribute: StrOrBytesPath, value: ReadableBuffer, flags: int = ..., *, follow_symlinks: bool = ...
         ) -> None: ...
 
 def abort() -> NoReturn: ...
@@ -810,6 +818,10 @@ _ExecVArgs: TypeAlias = (
     | list[str | PathLike[Any]]
     | list[bytes | str | PathLike[Any]]
 )
+# Depending on the OS, the keys and values are passed either to
+# PyUnicode_FSDecoder (which accepts str | ReadableBuffer) or to
+# PyUnicode_FSConverter (which accepts StrOrBytesPath). For simplicity,
+# we limit to str | bytes.
 _ExecEnv: TypeAlias = Mapping[bytes, bytes | str] | Mapping[str, bytes | str]
 
 def execv(__path: StrOrBytesPath, __argv: _ExecVArgs) -> NoReturn: ...