diff --git a/.isort.cfg b/.isort.cfg
new file mode 100644
index 00000000..77bd0559
--- /dev/null
+++ b/.isort.cfg
@@ -0,0 +1,3 @@
+[settings]
+known_standard_libary=posixpath
+known_third_party=gunicorn,passlib,pkg_resources,pytest,pytest_cov,vobject
diff --git a/radicale/app/__init__.py b/radicale/app/__init__.py
index 5e5a81c5..3c2930bf 100644
--- a/radicale/app/__init__.py
+++ b/radicale/app/__init__.py
@@ -28,6 +28,7 @@ import base64
 import datetime
 import io
 import logging
+import posixpath
 import pprint
 import random
 import time
@@ -52,8 +53,6 @@ from radicale.app.put import ApplicationPutMixin
 from radicale.app.report import ApplicationReportMixin
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 VERSION = pkg_resources.get_distribution("radicale").version
 
 
diff --git a/radicale/app/get.py b/radicale/app/get.py
index d38723e5..6c0e71da 100644
--- a/radicale/app/get.py
+++ b/radicale/app/get.py
@@ -17,14 +17,13 @@
 # You should have received a copy of the GNU General Public License
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
+import posixpath
 from http import client
 from urllib.parse import quote
 
 from radicale import httputils, pathutils, storage, xmlutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 def propose_filename(collection):
     """Propose a filename for a collection."""
diff --git a/radicale/app/mkcalendar.py b/radicale/app/mkcalendar.py
index 129b058d..11e01232 100644
--- a/radicale/app/mkcalendar.py
+++ b/radicale/app/mkcalendar.py
@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
+import posixpath
 import socket
 from http import client
 
@@ -25,8 +26,6 @@ from radicale import item as radicale_item
 from radicale import pathutils, storage, xmlutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 class ApplicationMkcalendarMixin:
     def do_MKCALENDAR(self, environ, base_prefix, path, user):
diff --git a/radicale/app/mkcol.py b/radicale/app/mkcol.py
index e6d3dda6..6771546c 100644
--- a/radicale/app/mkcol.py
+++ b/radicale/app/mkcol.py
@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
+import posixpath
 import socket
 from http import client
 
@@ -25,8 +26,6 @@ from radicale import item as radicale_item
 from radicale import pathutils, storage, xmlutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 class ApplicationMkcolMixin:
     def do_MKCOL(self, environ, base_prefix, path, user):
diff --git a/radicale/app/move.py b/radicale/app/move.py
index 3e20df12..79155b5f 100644
--- a/radicale/app/move.py
+++ b/radicale/app/move.py
@@ -17,14 +17,13 @@
 # You should have received a copy of the GNU General Public License
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
+import posixpath
 from http import client
 from urllib.parse import urlparse
 
 from radicale import httputils, pathutils, storage
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 class ApplicationMoveMixin:
     def do_MOVE(self, environ, base_prefix, path, user):
diff --git a/radicale/app/propfind.py b/radicale/app/propfind.py
index bcaa80c9..c67a1f4b 100644
--- a/radicale/app/propfind.py
+++ b/radicale/app/propfind.py
@@ -18,6 +18,7 @@
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
 import itertools
+import posixpath
 import socket
 from http import client
 from xml.etree import ElementTree as ET
@@ -25,8 +26,6 @@ from xml.etree import ElementTree as ET
 from radicale import httputils, pathutils, rights, storage, xmlutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 def xml_propfind(base_prefix, path, xml_request, allowed_items, user):
     """Read and answer PROPFIND requests.
diff --git a/radicale/app/put.py b/radicale/app/put.py
index 9fd7dfee..0e693e62 100644
--- a/radicale/app/put.py
+++ b/radicale/app/put.py
@@ -18,6 +18,7 @@
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
 import itertools
+import posixpath
 import socket
 import sys
 from http import client
@@ -29,8 +30,6 @@ from radicale import item as radicale_item
 from radicale import pathutils, storage, xmlutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 class ApplicationPutMixin:
     def do_PUT(self, environ, base_prefix, path, user):
diff --git a/radicale/app/report.py b/radicale/app/report.py
index 8c915fd4..8186ad73 100644
--- a/radicale/app/report.py
+++ b/radicale/app/report.py
@@ -18,6 +18,7 @@
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
 import contextlib
+import posixpath
 import socket
 from http import client
 from urllib.parse import unquote, urlparse
@@ -27,8 +28,6 @@ from radicale import httputils, pathutils, storage, xmlutils
 from radicale.item import filter as radicale_filter
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 def xml_report(base_prefix, path, xml_request, collection, unlock_storage_fn):
     """Read and answer REPORT requests.
diff --git a/radicale/pathutils.py b/radicale/pathutils.py
index eee3e6d8..5faaa90e 100644
--- a/radicale/pathutils.py
+++ b/radicale/pathutils.py
@@ -18,10 +18,9 @@
 
 import contextlib
 import os
+import posixpath
 import threading
 
-import posixpath  # isort:skip
-
 if os.name == "nt":
     import ctypes
     import ctypes.wintypes
diff --git a/radicale/storage/multifilesystem/discover.py b/radicale/storage/multifilesystem/discover.py
index f41cf358..e2992bfc 100644
--- a/radicale/storage/multifilesystem/discover.py
+++ b/radicale/storage/multifilesystem/discover.py
@@ -18,12 +18,11 @@
 
 import contextlib
 import os
+import posixpath
 
 from radicale import pathutils
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 
 class CollectionDiscoverMixin:
     @classmethod
diff --git a/radicale/tests/__init__.py b/radicale/tests/__init__.py
index 41ed0473..41a8eda9 100644
--- a/radicale/tests/__init__.py
+++ b/radicale/tests/__init__.py
@@ -25,8 +25,9 @@ import os
 import sys
 from io import BytesIO
 
-import radicale
 from pytest_cov import embed
+
+import radicale
 from radicale import server
 
 # Measure coverage of forked processes
diff --git a/radicale/tests/test_auth.py b/radicale/tests/test_auth.py
index a655b25a..988d2987 100644
--- a/radicale/tests/test_auth.py
+++ b/radicale/tests/test_auth.py
@@ -26,12 +26,12 @@ import os
 import shutil
 import tempfile
 
+import pytest
+
 from radicale import Application, config
 
 from .test_base import BaseTest
 
-import pytest  # isort:skip
-
 
 class TestBaseAuthRequests(BaseTest):
     """Tests basic requests with auth.
diff --git a/radicale/tests/test_base.py b/radicale/tests/test_base.py
index dab31e25..aa0ef853 100644
--- a/radicale/tests/test_base.py
+++ b/radicale/tests/test_base.py
@@ -22,21 +22,20 @@ Radicale tests with simple requests.
 
 import base64
 import os
+import posixpath
 import shutil
 import sys
 import tempfile
 import xml.etree.ElementTree as ET
 from functools import partial
 
+import pytest
+
 from radicale import Application, config, storage
 
 from . import BaseTest
 from .helpers import get_file_content
 
-import posixpath  # isort:skip
-
-import pytest  # isort:skip
-
 
 class BaseRequestsMixIn:
     """Tests with simple requests."""
diff --git a/radicale/tests/test_server.py b/radicale/tests/test_server.py
index 509cb22c..564287e5 100644
--- a/radicale/tests/test_server.py
+++ b/radicale/tests/test_server.py
@@ -32,12 +32,12 @@ from configparser import ConfigParser
 from urllib import request
 from urllib.error import HTTPError, URLError
 
+import pytest
+
 from radicale import config, server
 
 from .helpers import get_file_path
 
-import pytest  # isort:skip
-
 try:
     import gunicorn
 except ImportError:
diff --git a/radicale/web/internal.py b/radicale/web/internal.py
index de8b6ed4..7c9fa4a3 100644
--- a/radicale/web/internal.py
+++ b/radicale/web/internal.py
@@ -15,6 +15,7 @@
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import posixpath
 import time
 from http import client
 
@@ -23,8 +24,6 @@ import pkg_resources
 from radicale import httputils, pathutils, web
 from radicale.log import logger
 
-import posixpath  # isort:skip
-
 MIMETYPES = {
     ".css": "text/css",
     ".eot": "application/vnd.ms-fontobject",