diff --git a/doc/sphinx/development.rst b/doc/sphinx/development.rst
index 1db273da..067b8bfd 100644
--- a/doc/sphinx/development.rst
+++ b/doc/sphinx/development.rst
@@ -178,15 +178,23 @@ Hack, Hack, Hack
 
 .. note::
 
-    	Follow the Style Guide, basically `PEP 8 <https://www.python.org/dev/peps/pep-0008/>`_.
+      Follow the Style Guide, basically `PEP 8 <https://www.python.org/dev/peps/pep-0008/>`_.
 
-      We prefer to use double quotes and allow a max. line length of 99 characters.
+      Since version 3.x source formatting rules are delegated to the
+      `Black library <https://black.readthedocs.io/en/stable/>`_.
 
       Failing tests or not follwing PEP 8 will break builds on
       `travis <https://travis-ci.org/mar10/wsgidav>`_ and therefore be
-      automatically rejected.
+      automatically rejected:
 
-      Run ``$ flake8`` and ``$ tox`` frequently and before you commit!
+        - Run ``$ tox -e black`` to re-format the code, or
+          `look for plugins for your favorite editor <https://black.readthedocs.io/en/stable/editor_integration.html>`_
+          that format on-save.
+
+        - Run ``$ tox -e check`` frequently and before you commit.
+
+        - Don't forget to run ``$ tox`` to run the hole test suite before
+          you commit.
 
 
 Test, Test, Test
diff --git a/tox.ini b/tox.ini
index a6a53cbe..a829f5ea 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 basepython = python3.6
 #envlist = clean, py27, py34, py35, stats
-envlist = black, py27, py34, py35, py36, py37
+envlist = check, py27, py34, py35, py36, py37
 
 [testenv]
 passenv = LC_ALL LANG TRAVIS TRAVIS_BRANCH TRAVIS_OS_NAME TRAVIS_BUILD_ID
@@ -27,16 +27,31 @@ deps =
     requests
     webtest
 
-[testenv:black]
+
+[testenv:check]
 description = Check Black formatting compliance and add flake8-bugbear checks
 basepython = python3.6
+changedir = {toxinidir}
+skip_install = true
 deps =
     black
     flake8-bugbear
 commands =
-    black --check wsgidav tests
+    black --check --diff wsgidav tests
     flake8 wsgidav tests
 
+
+[testenv:black]
+description = Reformat python code using Black
+basepython = python3.6
+changedir = {toxinidir}
+skip_install = true
+deps =
+    black
+commands =
+    black wsgidav tests
+
+
 [testenv:docs]
 description = Build Sphinx documentation (output directory: docs/sphinx-build)
 basepython = python3.6
@@ -49,6 +64,7 @@ commands =
     # http://www.sphinx-doc.org/en/master/man/sphinx-build.html
     sphinx-build -b html sphinx sphinx-build
 
+
 # [testenv:clean]
 # commands =
 #     coverage erase
diff --git a/wsgidav/dav_provider.py b/wsgidav/dav_provider.py
index 43a7eaba..21423481 100644
--- a/wsgidav/dav_provider.py
+++ b/wsgidav/dav_provider.py
@@ -680,16 +680,10 @@ def get_property_value(self, name):
 
         elif name.startswith("{DAV:}"):
             # Standard live property (raises HTTP_NOT_FOUND if not supported)
-            if (
-                name == "{DAV:}creationdate"
-                and self.get_creation_date() is not None
-            ):
+            if name == "{DAV:}creationdate" and self.get_creation_date() is not None:
                 # Note: uses RFC3339 format (ISO 8601)
                 return util.get_rfc3339_time(self.get_creation_date())
-            elif (
-                name == "{DAV:}getcontenttype"
-                and self.get_content_type() is not None
-            ):
+            elif name == "{DAV:}getcontenttype" and self.get_content_type() is not None:
                 return self.get_content_type()
             elif name == "{DAV:}resourcetype":
                 if self.is_collection:
@@ -698,8 +692,7 @@ def get_property_value(self, name):
                     return resourcetypeEL
                 return ""
             elif (
-                name == "{DAV:}getlastmodified"
-                and self.get_last_modified() is not None
+                name == "{DAV:}getlastmodified" and self.get_last_modified() is not None
             ):
                 # Note: uses RFC1123 format
                 return util.get_rfc1123_time(self.get_last_modified())
@@ -711,9 +704,7 @@ def get_property_value(self, name):
                 return str(self.get_content_length())
             elif name == "{DAV:}getetag" and self.get_etag() is not None:
                 return self.get_etag()
-            elif (
-                name == "{DAV:}displayname" and self.get_display_name() is not None
-            ):
+            elif name == "{DAV:}displayname" and self.get_display_name() is not None:
                 return self.get_display_name()
 
             # Unsupported, no persistence available, or property not found