diff --git a/third_party/2and3/mypy_extensions.pyi b/third_party/2and3/mypy_extensions.pyi
index f42162c0e..19d99cc9d 100644
--- a/third_party/2and3/mypy_extensions.pyi
+++ b/third_party/2and3/mypy_extensions.pyi
@@ -1,7 +1,8 @@
 import abc
 import sys
 from typing import (
-    Dict, Type, TypeVar, Optional, Union, Any, Generic, Mapping, ItemsView, KeysView, ValuesView
+    Dict, Type, TypeVar, Optional, Union, Any, Generic, Mapping, ItemsView, KeysView, ValuesView,
+    Callable,
 )
 
 _T = TypeVar('_T')
@@ -41,4 +42,6 @@ NoReturn = Union[None]  # Deprecated: Use typing.NoReturn instead.
 # when a Type[_T] is expected, so we can't give it the type we want
 def trait(cls: Any) -> Any: ...
 
+def mypyc_attr(*attrs: str, **kwattrs: object) -> Callable[[_T], _T]: ...
+
 class FlexibleAlias(Generic[_T, _U]): ...