diff --git a/tools/lint-all b/tools/lint-all
index b75bd95e65..b4dab921a1 100755
--- a/tools/lint-all
+++ b/tools/lint-all
@@ -12,7 +12,7 @@ import traceback
 
 try:
     import lister
-    from typing import cast, Any, Callable, Dict, List, Optional, Generator, Tuple
+    from typing import cast, Any, Callable, Dict, Iterator, List, Optional, Tuple
 except ImportError as e:
     print("ImportError: {}".format(e))
     print("You need to run the Zulip linters inside a Zulip dev environment.")
@@ -38,7 +38,7 @@ zproject/test_settings.py
 
 @contextmanager
 def bright_red_output():
-    # type: () -> Generator[None, None, None]
+    # type: () -> Iterator[None]
     # Make the lint output bright red
     sys.stdout.write('\x1B[1;31m')
     sys.stdout.flush()
diff --git a/zerver/lib/context_managers.py b/zerver/lib/context_managers.py
index a31d174dbb..a20b7a1acc 100644
--- a/zerver/lib/context_managers.py
+++ b/zerver/lib/context_managers.py
@@ -6,11 +6,11 @@ from __future__ import absolute_import
 
 import fcntl
 from contextlib import contextmanager
-from typing import Generator
+from typing import Iterator
 
 @contextmanager
 def flock(lockfile, shared=False):
-    # type: (int, bool) -> Generator[None, None, None]
+    # type: (int, bool) -> Iterator[None]
     """Lock a file object using flock(2) for the duration of a 'with' statement.
 
        If shared is True, use a LOCK_SH lock, otherwise LOCK_EX."""
@@ -23,7 +23,7 @@ def flock(lockfile, shared=False):
 
 @contextmanager
 def lockfile(filename, shared=False):
-    # type: (str, bool) -> Generator[None, None, None]
+    # type: (str, bool) -> Iterator[None]
     """Lock a file using flock(2) for the duration of a 'with' statement.
 
        If shared is True, use a LOCK_SH lock, otherwise LOCK_EX.
diff --git a/zerver/lib/test_classes.py b/zerver/lib/test_classes.py
index 64afd8f77d..d435ff0bec 100644
--- a/zerver/lib/test_classes.py
+++ b/zerver/lib/test_classes.py
@@ -1,7 +1,7 @@
 from __future__ import absolute_import
 from __future__ import print_function
 from contextlib import contextmanager
-from typing import (cast, Any, Callable, Dict, Generator, Iterable, List, Mapping, Optional,
+from typing import (cast, Any, Callable, Dict, Iterable, Iterator, List, Mapping, Optional,
     Sized, Tuple, Union)
 
 from django.core.urlresolvers import resolve
@@ -406,7 +406,7 @@ class ZulipTestCase(TestCase):
 
     @contextmanager
     def simulated_markdown_failure(self):
-        # type: () -> Generator[None, None, None]
+        # type: () -> Iterator[None]
         '''
         This raises a failure inside of the try/except block of
         bugdown.__init__.do_convert.
diff --git a/zerver/lib/test_helpers.py b/zerver/lib/test_helpers.py
index bd479bfe2d..c2bae7b0ba 100644
--- a/zerver/lib/test_helpers.py
+++ b/zerver/lib/test_helpers.py
@@ -1,8 +1,8 @@
 from __future__ import absolute_import
 from __future__ import print_function
 from contextlib import contextmanager
-from typing import (cast, Any, Callable, Dict, Generator, Iterable, List, Mapping, Optional,
-    Sized, Tuple, Union)
+from typing import (cast, Any, Callable, Dict, Generator, Iterable, Iterator, List, Mapping,
+    Optional, Sized, Tuple, Union)
 
 from django.core.urlresolvers import LocaleRegexURLResolver
 from django.conf import settings
@@ -62,7 +62,7 @@ import six
 
 @contextmanager
 def simulated_queue_client(client):
-    # type: (type) -> Generator[None, None, None]
+    # type: (type) -> Iterator[None]
     real_SimpleQueueClient = queue_processors.SimpleQueueClient
     queue_processors.SimpleQueueClient = client # type: ignore # https://github.com/JukkaL/mypy/issues/1152
     yield
@@ -70,7 +70,7 @@ def simulated_queue_client(client):
 
 @contextmanager
 def tornado_redirected_to_list(lst):
-    # type: (List[Mapping[str, Any]]) -> Generator[None, None, None]
+    # type: (List[Mapping[str, Any]]) -> Iterator[None]
     real_event_queue_process_notification = event_queue.process_notification
     event_queue.process_notification = lst.append
     yield