diff --git a/stdlib/2/__builtin__.pyi b/stdlib/2/__builtin__.pyi
index a4d6b03625f4..8ac0056f938c 100644
--- a/stdlib/2/__builtin__.pyi
+++ b/stdlib/2/__builtin__.pyi
@@ -1315,10 +1315,12 @@ def oct(__i: int) -> str: ...  # TODO __index__
 
 if sys.version_info >= (3, 6):
     def open(file: Union[str, bytes, int, _PathLike], mode: str = ..., buffering: int = ..., encoding: Optional[str] = ...,
-             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...) -> IO[Any]: ...
+             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...,
+             opener: Optional[Callable[[str, int], int]] = ...) -> IO[Any]: ...
 elif sys.version_info >= (3,):
     def open(file: Union[str, bytes, int], mode: str = ..., buffering: int = ..., encoding: Optional[str] = ...,
-             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...) -> IO[Any]: ...
+             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...,
+             opener: Optional[Callable[[str, int], int]] = ...) -> IO[Any]: ...
 else:
     def open(name: Union[unicode, int], mode: unicode = ..., buffering: int = ...) -> BinaryIO: ...
 
diff --git a/stdlib/2and3/builtins.pyi b/stdlib/2and3/builtins.pyi
index a4d6b03625f4..8ac0056f938c 100644
--- a/stdlib/2and3/builtins.pyi
+++ b/stdlib/2and3/builtins.pyi
@@ -1315,10 +1315,12 @@ def oct(__i: int) -> str: ...  # TODO __index__
 
 if sys.version_info >= (3, 6):
     def open(file: Union[str, bytes, int, _PathLike], mode: str = ..., buffering: int = ..., encoding: Optional[str] = ...,
-             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...) -> IO[Any]: ...
+             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...,
+             opener: Optional[Callable[[str, int], int]] = ...) -> IO[Any]: ...
 elif sys.version_info >= (3,):
     def open(file: Union[str, bytes, int], mode: str = ..., buffering: int = ..., encoding: Optional[str] = ...,
-             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...) -> IO[Any]: ...
+             errors: Optional[str] = ..., newline: Optional[str] = ..., closefd: bool = ...,
+             opener: Optional[Callable[[str, int], int]] = ...) -> IO[Any]: ...
 else:
     def open(name: Union[unicode, int], mode: unicode = ..., buffering: int = ...) -> BinaryIO: ...