diff --git a/stdlib/2/os/__init__.pyi b/stdlib/2/os/__init__.pyi
index 2c66dc79d..da2a35dd1 100644
--- a/stdlib/2/os/__init__.pyi
+++ b/stdlib/2/os/__init__.pyi
@@ -192,7 +192,7 @@ def lseek(fd: int, pos: int, how: int) -> int: ...
 def open(file: _PathType, flags: int, mode: int = ...) -> int: ...
 def pipe() -> Tuple[int, int]: ...
 def read(fd: int, n: int) -> bytes: ...
-def write(fd: int, string: bytes) -> int: ...
+def write(fd: int, string: Union[bytes, buffer]) -> int: ...
 def access(path: _PathType, mode: int) -> bool: ...
 def chdir(path: _PathType) -> None: ...
 def fchdir(fd: int) -> None: ...