diff --git a/third_party/2and3/yaml/__init__.pyi b/third_party/2and3/yaml/__init__.pyi
index 4a5d2cda5a49..47d490e212a5 100644
--- a/third_party/2and3/yaml/__init__.pyi
+++ b/third_party/2and3/yaml/__init__.pyi
@@ -1,4 +1,4 @@
-from typing import Any, Iterator, Sequence, Union, IO
+from typing import Any, Iterator, Optional, Sequence, Union, IO
 from yaml.error import *  # noqa: F403
 from yaml.tokens import *  # noqa: F403
 from yaml.events import *  # noqa: F403
@@ -22,8 +22,8 @@ def safe_load_all(stream: Union[str, IO[str]]) -> Iterator[Any]: ...
 def emit(events, stream=..., Dumper=..., canonical=..., indent=..., width=..., allow_unicode=..., line_break=...): ...
 def serialize_all(nodes, stream=..., Dumper=..., canonical=..., indent=..., width=..., allow_unicode=..., line_break=..., encoding=..., explicit_start=..., explicit_end=..., version=..., tags=...): ...
 def serialize(node, stream=..., Dumper=..., **kwds): ...
-def dump_all(documents: Sequence[Any], stream: IO[str]=..., Dumper=..., default_style=..., default_flow_style=..., canonical=..., indent=..., width=..., allow_unicode=..., line_break=..., encoding=..., explicit_start=..., explicit_end=..., version=..., tags=...) -> Any: ...
-def dump(data: Any, stream: IO[str]=..., Dumper=..., **kwds) -> Any: ...
+def dump_all(documents: Sequence[Any], stream: Optional[IO[str]]=..., Dumper=..., default_style=..., default_flow_style=..., canonical=..., indent=..., width=..., allow_unicode=..., line_break=..., encoding=..., explicit_start=..., explicit_end=..., version=..., tags=...) -> Any: ...
+def dump(data: Any, stream: Optional[IO[str]]=..., Dumper=..., **kwds) -> Any: ...
 def safe_dump_all(documents: Sequence[Any], stream: IO[str]=..., **kwds) -> Any: ...
 def safe_dump(data: Any, stream: IO[str]=..., **kwds) -> Any: ...
 def add_implicit_resolver(tag, regexp, first=..., Loader=..., Dumper=...): ...