diff --git a/third_party/2and3/mypy_extensions.pyi b/third_party/2and3/mypy_extensions.pyi
index 05400c8c7..1c5b46b9c 100644
--- a/third_party/2and3/mypy_extensions.pyi
+++ b/third_party/2and3/mypy_extensions.pyi
@@ -1,8 +1,28 @@
-from typing import Dict, Type, TypeVar, Optional, Union, Any, Generic
+import abc
+import sys
+from typing import (
+    Dict, Type, TypeVar, Optional, Union, Any, Generic, Mapping, ItemsView, KeysView, ValuesView
+)
 
 _T = TypeVar('_T')
 _U = TypeVar('_U')
 
+# Internal mypy fallback type for all typed dicts (does not exist at runtime)
+class _TypedDict(Mapping[str, object], metaclass=abc.ABCMeta):
+    def copy(self: _T) -> _T: ...
+    # Using NoReturn so that only calls using mypy plugin hook that specialize the signature
+    # can go through.
+    def setdefault(self, k: NoReturn, default: object) -> object: ...
+    # Mypy plugin hook for 'pop' expects that 'default' has a type variable type.
+    def pop(self, k: NoReturn, default: _T = ...) -> object: ...
+    def update(self: _T, __m: _T) -> None: ...
+    if sys.version_info < (3, 0):
+        def has_key(self) -> bool: ...
+        def viewitems(self) -> ItemsView[str, object]: ...
+        def viewkeys(self) -> KeysView[str]: ...
+        def viewvalues(self) -> ValuesView[object]: ...
+    def __delitem__(self, k: NoReturn) -> None: ...
+
 def TypedDict(typename: str, fields: Dict[str, Type[_T]], total: bool = ...) -> Type[dict]: ...
 
 def Arg(type: _T = ..., name: Optional[str] = ...) -> _T: ...