diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index b9969fe6f..d2861677c 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -4,7 +4,12 @@ Changelog
 *unreleased*
 ~~~~~~~~~~~~
 
-* Run [isort](https://pypi.org/project/isort/) over the code base (:issue:`377`)
+No unreleased changes.
+
+20.9 - 2021-01-29
+~~~~~~~~~~~~~~~~~
+
+* Run `isort <https://pypi.org/project/isort/>`_ over the code base (:issue:`377`)
 * Add support for the ``macosx_10_*_universal2`` platform tags (:issue:`379`)
 * Introduce ``packaging.utils.parse_wheel_filename()`` and ``parse_sdist_filename()``
   (:issue:`387` and :issue:`389`)
diff --git a/noxfile.py b/noxfile.py
index 732abb6bd..af88400a5 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -144,17 +144,17 @@ def release(session):
         diff = "\n".join(diff_generator)
         session.error(f"Got the wrong files:\n{diff}")
 
-    # Get back out into master.
-    session.run("git", "checkout", "-q", "master", external=True)
+    # Get back out into main.
+    session.run("git", "checkout", "-q", "main", external=True)
 
     # Check and upload distribution files.
     session.run("twine", "check", *files)
 
     # Push the commits and tag.
     # NOTE: The following fails if pushing to the branch is not allowed. This can
-    #       happen on GitHub, if the master branch is protected, there are required
+    #       happen on GitHub, if the main branch is protected, there are required
     #       CI checks and "Include administrators" is enabled on the protection.
-    session.run("git", "push", "upstream", "master", release_version, external=True)
+    session.run("git", "push", "upstream", "main", release_version, external=True)
 
     # Upload the distribution.
     session.run("twine", "upload", *files)
@@ -210,14 +210,14 @@ def _check_git_state(session, version_tag):
     )
     if result.stdout.rstrip() not in allowed_upstreams:
         session.error(f"git remote `upstream` is not one of {allowed_upstreams}")
-    # Ensure we're on master branch for cutting a release.
+    # Ensure we're on main branch for cutting a release.
     result = subprocess.run(
         ["git", "rev-parse", "--abbrev-ref", "HEAD"],
         capture_output=True,
         encoding="utf-8",
     )
-    if result.stdout != "master\n":
-        session.error(f"Not on master branch: {result.stdout!r}")
+    if result.stdout != "main\n":
+        session.error(f"Not on main branch: {result.stdout!r}")
 
     # Ensure there are no uncommitted changes.
     result = subprocess.run(
diff --git a/packaging/__about__.py b/packaging/__about__.py
index db7fe5876..b43f363ab 100644
--- a/packaging/__about__.py
+++ b/packaging/__about__.py
@@ -18,7 +18,7 @@
 __summary__ = "Core utilities for Python packages"
 __uri__ = "https://github.com/pypa/packaging"
 
-__version__ = "20.9.dev0"
+__version__ = "20.10.dev0"
 
 __author__ = "Donald Stufft and individual contributors"
 __email__ = "donald@stufft.io"
diff --git a/packaging/version.py b/packaging/version.py
index 517d91f24..e3cfb6f92 100644
--- a/packaging/version.py
+++ b/packaging/version.py
@@ -372,12 +372,12 @@ def pre(self):
 
     @property
     def post(self):
-        # type: () -> Optional[Tuple[str, int]]
+        # type: () -> Optional[int]
         return self._version.post[1] if self._version.post else None
 
     @property
     def dev(self):
-        # type: () -> Optional[Tuple[str, int]]
+        # type: () -> Optional[int]
         return self._version.dev[1] if self._version.dev else None
 
     @property