diff --git a/stdlib/2/os/__init__.pyi b/stdlib/2/os/__init__.pyi
index 7041e1fbe..8e66b4849 100644
--- a/stdlib/2/os/__init__.pyi
+++ b/stdlib/2/os/__init__.pyi
@@ -291,7 +291,7 @@ if sys.platform != 'win32':
     # Unix only
     def fork() -> int: ...
     def forkpty() -> Tuple[int, int]: ...  # some flavors of Unix
-    def killpg(pgid: int, sig: int) -> None: ...
+    def killpg(__pgid: int, __signal: int) -> None: ...
     def nice(increment: int) -> int: ...
     def plock(op: int) -> None: ...  # ???op is int?