diff --git a/stdlib/os/__init__.pyi b/stdlib/os/__init__.pyi
index 2e8561501..4500a748d 100644
--- a/stdlib/os/__init__.pyi
+++ b/stdlib/os/__init__.pyi
@@ -390,9 +390,9 @@ if sys.platform != "win32":
     def getegid() -> int: ...
     def geteuid() -> int: ...
     def getgid() -> int: ...
-    def getgrouplist(user: str, gid: int) -> List[int]: ...
+    def getgrouplist(__user: str, __group: int) -> List[int]: ...
     def getgroups() -> List[int]: ...  # Unix only, behaves differently on Mac
-    def initgroups(username: str, gid: int) -> None: ...
+    def initgroups(__username: str, __gid: int) -> None: ...
     def getpgid(pid: int) -> int: ...
     def getpgrp() -> int: ...
     def getpriority(which: int, who: int) -> int: ...
@@ -552,11 +552,11 @@ if sys.platform != "win32":
     def pread(__fd: int, __length: int, __offset: int) -> bytes: ...
     def pwrite(__fd: int, __buffer: bytes, __offset: int) -> int: ...
     @overload
-    def sendfile(__out_fd: int, __in_fd: int, offset: Optional[int], count: int) -> int: ...
+    def sendfile(out_fd: int, in_fd: int, offset: Optional[int], count: int) -> int: ...
     @overload
     def sendfile(
-        __out_fd: int,
-        __in_fd: int,
+        out_fd: int,
+        in_fd: int,
         offset: int,
         count: int,
         headers: Sequence[bytes] = ...,