diff --git a/stdlib/3/shutil.pyi b/stdlib/3/shutil.pyi
index 13075979a..c0745e368 100644
--- a/stdlib/3/shutil.pyi
+++ b/stdlib/3/shutil.pyi
@@ -7,7 +7,7 @@ import sys
 # sometimes they only work partially (broken exception messages), and the test
 # cases don't use them.
 
-from typing import List, Iterable, Callable, Any, Tuple, Sequence, IO, AnyStr
+from typing import List, Iterable, Callable, Any, Tuple, Sequence, IO, AnyStr, Optional
 
 def copyfileobj(fsrc: IO[AnyStr], fdst: IO[AnyStr],
                 length: int = ...) -> None: ...
@@ -48,4 +48,4 @@ def register_unpack_format(name: str, extensions: List[str], function: Any,
 def unregister_unpack_format(name: str) -> None: ...
 def get_unpack_formats() -> List[Tuple[str, List[str], str]]: ...
 
-def which(cmd: str, mode: int = ..., path: str = ...): ...
+def which(cmd: str, mode: int = ..., path: str = ...) -> Optional[str]: ...