diff --git a/stdlib/3/tokenize.pyi b/stdlib/3/tokenize.pyi
index b3c5fd964..60b6ec97e 100644
--- a/stdlib/3/tokenize.pyi
+++ b/stdlib/3/tokenize.pyi
@@ -41,7 +41,7 @@ class Untokenizer:
 def untokenize(iterable: Iterable[_Token]) -> Any: ...
 def detect_encoding(readline: Callable[[], bytes]) -> Tuple[str, Sequence[bytes]]: ...
 def tokenize(readline: Callable[[], bytes]) -> Generator[TokenInfo, None, None]: ...
-def generate_tokens(readline: Callable[[], str]) -> Generator[TokenInfo, None, None]: ...
+def generate_tokens(readline: Callable[[], bytes]) -> Generator[TokenInfo, None, None]: ...  # undocumented
 
 if sys.version_info >= (3, 6):
     from os import PathLike