diff --git a/linters-requirements.txt b/linters-requirements.txt
index 73461fefe..4fd14e840 100644
--- a/linters-requirements.txt
+++ b/linters-requirements.txt
@@ -1,7 +1,7 @@
 # pep8 and flake8 requirements
 
 ansible-lint==4.2.0        # MIT
-flake8==3.3.0              # MIT
+flake8>=3.8.1              # MIT
 flake8-import-order==0.12  # LGPLv3
 mypy>=0.740                # MIT
 pylint>=1.9,<2.5.0  # GPLv2
diff --git a/tobiko/shell/sh/_local.py b/tobiko/shell/sh/_local.py
index d350194d4..c105220a1 100644
--- a/tobiko/shell/sh/_local.py
+++ b/tobiko/shell/sh/_local.py
@@ -66,7 +66,7 @@ class LocalExecutePathFixture(_path.ExecutePathFixture):
 
     executable_dirs = [os.path.realpath(os.path.join(d, 'bin'))
                        for d in [sys.prefix, sys.exec_prefix]]
-    environ = os.environ
+    environ = dict(os.environ)
 
 
 class LocalShellProcessFixture(_process.ShellProcessFixture):
diff --git a/tobiko/shell/sh/_path.py b/tobiko/shell/sh/_path.py
index 54484a526..35144ba5b 100644
--- a/tobiko/shell/sh/_path.py
+++ b/tobiko/shell/sh/_path.py
@@ -15,6 +15,8 @@
 #    under the License.
 from __future__ import absolute_import
 
+import typing  # noqa
+
 from oslo_log import log
 
 import tobiko
diff --git a/tobiko/shell/ssh/_client.py b/tobiko/shell/ssh/_client.py
index 952cae3a6..a61ef380b 100644
--- a/tobiko/shell/ssh/_client.py
+++ b/tobiko/shell/ssh/_client.py
@@ -198,7 +198,7 @@ def _items_from_object(obj, schema):
 
 
 def exclude_mapping_items(mapping, exclude):
-        # Exclude parameters that are already in target dictionary
+    """Exclude parameters that are already in target dictionary"""
     return {key: value
             for key, value in mapping.items()
             if key not in exclude}