diff --git a/third_party/2and3/mypy_extensions.pyi b/third_party/2and3/mypy_extensions.pyi
index 6c57954d8a81..83a452b73c29 100644
--- a/third_party/2and3/mypy_extensions.pyi
+++ b/third_party/2and3/mypy_extensions.pyi
@@ -1,6 +1,24 @@
-from typing import Dict, Type, TypeVar
+from typing import Dict, Type, TypeVar, Optional, Any
 
 T = TypeVar('T')
 
 
 def TypedDict(typename: str, fields: Dict[str, Type[T]]) -> Type[dict]: ...
+
+class Arg(object):
+    def __init__(name: Optional[str]=...,
+                 typ: Type[T]=...,
+                 keyword_only: Optional[bool]=...) -> None:
+        ...
+
+class DefaultArg(object):
+    def __init__(name: Optional[str]=...,
+                 typ: Type[T]=...,
+                 keyword_only: Optional[bool]=...) -> None:
+        ...
+
+class StarArg(object):
+    def __init__(typ: Type[T]=...) -> None: ...
+
+class KwArg(object):
+    def __init__(typ: Type[T]=...) -> None: ...