diff --git a/stdlib/2/unittest.pyi b/stdlib/2/unittest.pyi
index bcd13e15d001..e8b1b7f62273 100644
--- a/stdlib/2/unittest.pyi
+++ b/stdlib/2/unittest.pyi
@@ -4,6 +4,7 @@
 
 # Only a subset of functionality is included.
 
+from mypy_extensions import NoReturn
 from typing import (Any, Callable, Dict, FrozenSet, Iterable, List, Optional,
                     overload, Pattern, Sequence, Set, TextIO, Tuple, Type,
                     TypeVar, Union)
@@ -131,7 +132,7 @@ class TestCase(Testable):
                          msg: object = ...) -> None: ...
     def assertNotIsInstance(self, obj: Any, cls: Union[type, Tuple[type, ...]],
                             msg: object = ...) -> None: ...
-    def fail(self, msg: object = ...) -> None: ...
+    def fail(self, msg: object = ...) -> NoReturn: ...
     def countTestCases(self) -> int: ...
     def defaultTestResult(self) -> TestResult: ...
     def id(self) -> str: ...
diff --git a/stdlib/3/unittest/__init__.pyi b/stdlib/3/unittest/__init__.pyi
index 6c0e409d9c7c..7bbbb0d40676 100644
--- a/stdlib/3/unittest/__init__.pyi
+++ b/stdlib/3/unittest/__init__.pyi
@@ -1,9 +1,10 @@
 # Stubs for unittest
 
+from mypy_extensions import NoReturn
 from typing import (
-    Any, Callable, Dict, Iterable, Iterator, List, Optional, Pattern, Sequence,
-    Set, FrozenSet, TextIO, Tuple, Type, TypeVar, Union, Generic,
-    overload, ContextManager
+    Any, Callable, ContextManager, Dict, FrozenSet, Generic, Iterable, Iterator,
+    List, Optional, overload, Pattern, Sequence, Set, TextIO, Tuple, Type,
+    TypeVar, Union
 )
 import logging
 import sys
@@ -134,7 +135,7 @@ class TestCase:
                        second: Union[Set[Any], FrozenSet[Any]], msg: Any = ...) -> None: ...
     def assertDictEqual(self, first: Dict[Any, Any], second: Dict[Any, Any],
                         msg: Any = ...) -> None: ...
-    def fail(self, msg: Any = ...) -> None: ...
+    def fail(self, msg: Any = ...) -> NoReturn: ...
     def countTestCases(self) -> int: ...
     def defaultTestResult(self) -> TestResult: ...
     def id(self) -> str: ...