diff --git a/.github/workflows/CI.yaml b/.github/workflows/CI.yaml
index 5bef62e7..b3a7532b 100644
--- a/.github/workflows/CI.yaml
+++ b/.github/workflows/CI.yaml
@@ -10,7 +10,7 @@ jobs:
     # https://github.com/actions/python-versions/blob/main/versions-manifest.json
     strategy:
       matrix:
-        os: [macos-latest, ubuntu-latest]
+        os: [macos-latest, ubuntu-20.04]
         python-version: [3.6, 3.7, 3.8, pypy-3.7]
     steps:
       - uses: actions/checkout@v2
@@ -21,7 +21,7 @@ jobs:
       - name: Install Requirements
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 pylint pytest
+          pip install flake8==5.0.4 pylint pytest
           pip install -r requirements.txt
           pip install -r test/requirements.txt
           python setup.py install
diff --git a/README.rst b/README.rst
index 82f00804..2d3cc79f 100644
--- a/README.rst
+++ b/README.rst
@@ -26,6 +26,8 @@ command line::
 
     $ stone -h
 
+Stone requires Python 3.
+
 Alternative
 -----------
 
diff --git a/mypy-run.sh b/mypy-run.sh
index 119f2fd8..f3434374 100755
--- a/mypy-run.sh
+++ b/mypy-run.sh
@@ -6,4 +6,3 @@ EXCLUDE='(^example/|^ez_setup\.py$|^setup\.py$)'
 INCLUDE=$(git ls-files "$@" | grep '\.py$' | grep -Ev "$EXCLUDE" | tr '\n' '\0' | xargs -0 | cat)
 MYPY_CMD=mypy
 $MYPY_CMD $INCLUDE
-$MYPY_CMD --py2 $INCLUDE
diff --git a/mypy.ini b/mypy.ini
index 0fd85ed9..b2dd65f5 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,5 +1,4 @@
 [mypy]
 # follow_imports = False
 ignore_missing_imports = True
-show_none_errors = True
 strict_optional = True
diff --git a/setup.py b/setup.py
index 5977589a..ae41d750 100644
--- a/setup.py
+++ b/setup.py
@@ -22,9 +22,7 @@
     install_reqs += f.read().splitlines()
 
 setup_requires = [
-    # Pin pytest-runner to 5.2.0, since 5.3.0 uses `find_namespaces` directive, not supported in
-    # Python 2.7
-    'pytest-runner == 5.2.0',
+    'pytest-runner == 5.3.2',
 ]
 
 # WARNING: This imposes limitations on test/requirements.txt such that the
diff --git a/stone/backends/js_client.py b/stone/backends/js_client.py
index 14076850..728e38ae 100644
--- a/stone/backends/js_client.py
+++ b/stone/backends/js_client.py
@@ -5,13 +5,7 @@
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
     from stone.ir import ApiNamespace
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 from stone.backend import CodeBackend
 from stone.backends.js_helpers import (
diff --git a/stone/backends/js_types.py b/stone/backends/js_types.py
index 778bf11c..aa775c9e 100644
--- a/stone/backends/js_types.py
+++ b/stone/backends/js_types.py
@@ -22,14 +22,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
-
+import argparse
 
 _cmdline_parser = argparse.ArgumentParser(prog='js-types-backend')
 _cmdline_parser.add_argument(
diff --git a/stone/backends/obj_c_client.py b/stone/backends/obj_c_client.py
index c86253fa..91587aad 100644
--- a/stone/backends/obj_c_client.py
+++ b/stone/backends/obj_c_client.py
@@ -37,13 +37,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 _cmdline_parser = argparse.ArgumentParser(
     prog='objc-client-backend',
diff --git a/stone/backends/obj_c_types.py b/stone/backends/obj_c_types.py
index df07b445..350fd6ce 100644
--- a/stone/backends/obj_c_types.py
+++ b/stone/backends/obj_c_types.py
@@ -57,13 +57,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 _cmdline_parser = argparse.ArgumentParser(prog='obj-c-types-backend')
 _cmdline_parser.add_argument(
diff --git a/stone/backends/python_client.py b/stone/backends/python_client.py
index edc88fd3..2c2a2729 100644
--- a/stone/backends/python_client.py
+++ b/stone/backends/python_client.py
@@ -31,14 +31,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
-
+import argparse
 
 # This will be at the top of the generated file.
 base = """\
diff --git a/stone/backends/swift_client.py b/stone/backends/swift_client.py
index 6c2adfce..9228729b 100644
--- a/stone/backends/swift_client.py
+++ b/stone/backends/swift_client.py
@@ -25,13 +25,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 
 _cmdline_parser = argparse.ArgumentParser(
diff --git a/stone/backends/swift_types.py b/stone/backends/swift_types.py
index 572e4407..6e2baa9e 100644
--- a/stone/backends/swift_types.py
+++ b/stone/backends/swift_types.py
@@ -35,14 +35,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
-
+import argparse
 
 _cmdline_parser = argparse.ArgumentParser(prog='swift-types-backend')
 _cmdline_parser.add_argument(
diff --git a/stone/backends/tsd_client.py b/stone/backends/tsd_client.py
index 6c07b4f7..b51b6e78 100644
--- a/stone/backends/tsd_client.py
+++ b/stone/backends/tsd_client.py
@@ -7,13 +7,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 from stone.backend import CodeBackend
 from stone.backends.tsd_helpers import (
diff --git a/stone/backends/tsd_types.py b/stone/backends/tsd_types.py
index 3800c5f1..79690390 100644
--- a/stone/backends/tsd_types.py
+++ b/stone/backends/tsd_types.py
@@ -10,13 +10,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 from stone.ir import ApiNamespace
 from stone.ir import (
diff --git a/stone/cli.py b/stone/cli.py
index d6004ce7..53a1ac13 100644
--- a/stone/cli.py
+++ b/stone/cli.py
@@ -26,13 +26,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
+import argparse
 
 # These backends come by default
 _builtin_backends = (
diff --git a/stone/frontend/ir_generator.py b/stone/frontend/ir_generator.py
index f761ce5d..9a207416 100644
--- a/stone/frontend/ir_generator.py
+++ b/stone/frontend/ir_generator.py
@@ -9,19 +9,13 @@
 try:
     from inspect import getfullargspec as get_args
 except ImportError:
-    from inspect import getargspec as get_args
+    from inspect import getargspec as get_args  # type: ignore
 
 _MYPY = False
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-re = importlib.import_module(str('re'))  # type: typing.Any
+import re
 
 from ..ir import (
     Alias,
diff --git a/stone/ir/data_types.py b/stone/ir/data_types.py
index 0bd98dea..858c1510 100644
--- a/stone/ir/data_types.py
+++ b/stone/ir/data_types.py
@@ -689,7 +689,7 @@ def set_default(self, default):
     @property
     def default(self):
         if not self.has_default:
-            raise Exception('Type has no default')
+            raise ValueError('Type has no default')
         else:
             return self._default
 
@@ -1382,7 +1382,7 @@ def __init__(self, name, namespace, ast_node, closed):
 
     # TODO: Why is this a different signature than the parent? Is this
     # intentional?
-    def set_attributes(self, doc, fields,  # pylint: disable=arguments-differ
+    def set_attributes(self, doc, fields,
             parent_type=None, catch_all_field=None):
         """
         :param UnionField catch_all_field: The field designated as the
@@ -1475,7 +1475,6 @@ def _add_example(self, example):
             )
 
         # TODO: are we always guaranteed at least one field?
-        # pylint: disable=undefined-loop-variable
         try:
             field.data_type.check_example(example_field)
         except InvalidSpec as e:
@@ -1581,7 +1580,6 @@ def get_json_val(dt, val):
                 raise AssertionError('No example for label %r' % label)
 
             # TODO: are we always guaranteed at least one field?
-            # pylint: disable=undefined-loop-variable
             assert is_void_type(field.data_type)
             return Example(
                 field.name, field.doc, OrderedDict([('.tag', field.name)]))
diff --git a/test/test_backend.py b/test/test_backend.py
index 56a045ce..6a911cd4 100755
--- a/test/test_backend.py
+++ b/test/test_backend.py
@@ -29,14 +29,7 @@
 if _MYPY:
     import typing  # noqa: F401 # pylint: disable=import-error,unused-import,useless-suppression
 
-# Hack to get around some of Python 2's standard library modules that
-# accept ascii-encodable unicode literals in lieu of strs, but where
-# actually passing such literals results in errors with mypy --py2. See
-# <https://github.com/python/typeshed/issues/756> and
-# <https://github.com/python/mypy/issues/2536>.
-import importlib
-argparse = importlib.import_module(str('argparse'))  # type: typing.Any
-
+import argparse
 class _Tester(CodeBackend):
     """A no-op backend used to test helper methods."""
     def generate(self, api):
diff --git a/test/test_python_gen.py b/test/test_python_gen.py
index 6465f0a7..578ac0b1 100755
--- a/test/test_python_gen.py
+++ b/test/test_python_gen.py
@@ -1245,8 +1245,8 @@ def test_struct_equality_with_value(self):
         self.assertNotEqual(s, s_unequal)
 
     def test_struct_equality_with_different_types(self):
-        """Structs of different types that do not have an inheritance relationship are not considered
-        equal to each other."""
+        """Structs of different types that do not have an inheritance relationship are not
+        considered equal to each other."""
         s = self.decode(bv.Struct(self.ns.S), json.dumps({'f': 'F'}))
         t = self.decode(bv.Struct(self.ns.T), json.dumps({'f': 'F'}))
         self.assertNotEqual(s, t)
diff --git a/test/test_tsd_types.py b/test/test_tsd_types.py
index 49b8dda9..8595f76f 100644
--- a/test/test_tsd_types.py
+++ b/test/test_tsd_types.py
@@ -27,7 +27,7 @@
 from test.backend_test_util import _mock_output
 
 
-def _make_backend(target_folder_path, template_path, custom_args=None):
+def _make_backend(target_folder_path, template_path, custom_args=None):  # type: ignore
     # type: (typing.Text, typing.Text, typing.List) -> TSDTypesBackend
 
     args = Mock()
diff --git a/tox.ini b/tox.ini
index b8ef1502..a694f6ec 100644
--- a/tox.ini
+++ b/tox.ini
@@ -38,7 +38,7 @@ commands =
     pylint --rcfile=.pylintrc setup.py example stone test
 
 deps =
-    flake8
+    flake8<6
     pylint
     # This probably breaks on Windows. See
     # <https://github.com/tox-dev/tox/issues/384>.