diff --git a/stdlib/2/__builtin__.pyi b/stdlib/2/__builtin__.pyi
index db00c557ef22..72bfc3b9fcf5 100644
--- a/stdlib/2/__builtin__.pyi
+++ b/stdlib/2/__builtin__.pyi
@@ -1173,7 +1173,7 @@ else:
 def iter(iterable: Iterable[_T]) -> Iterator[_T]: ...
 @overload
 def iter(function: Callable[[], _T], sentinel: _T) -> Iterator[_T]: ...
-def isinstance(o: object, t: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
+def isinstance(o: Optional[object], t: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
 def issubclass(cls: type, classinfo: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
 def len(o: Sized) -> int: ...
 if sys.version_info >= (3,):
diff --git a/stdlib/2and3/builtins.pyi b/stdlib/2and3/builtins.pyi
index db00c557ef22..72bfc3b9fcf5 100644
--- a/stdlib/2and3/builtins.pyi
+++ b/stdlib/2and3/builtins.pyi
@@ -1173,7 +1173,7 @@ else:
 def iter(iterable: Iterable[_T]) -> Iterator[_T]: ...
 @overload
 def iter(function: Callable[[], _T], sentinel: _T) -> Iterator[_T]: ...
-def isinstance(o: object, t: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
+def isinstance(o: Optional[object], t: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
 def issubclass(cls: type, classinfo: Union[type, Tuple[Union[type, Tuple], ...]]) -> bool: ...
 def len(o: Sized) -> int: ...
 if sys.version_info >= (3,):