diff --git a/CHANGES b/CHANGES
index 56e84d4..9bf789f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,10 @@ Nodeenv changelog
 Version [unreleased]
 --------------------
 
+- The default configuration dump and README example omit options without
+  defaults, such as `mirror`, so they can be copied into a config file
+  without selecting a mirror named `None`
+  `#422 <https://github.com/ekalinin/nodeenv/issues/422>`_
 - Require Python 3.10 or later, matching the minimum version tested in CI.
   Update package classifiers and wheel tags, and remove the unused Python 2
   compatibility paths. Old Node.js source builds still require Python 2.7
@@ -35,8 +39,8 @@ Version [unreleased]
   text files (npm 8) and whose workspaces are missing (npm >= 9); the default
   `--npm=latest` no longer ends in a 404 there
   `#310 <https://github.com/ekalinin/nodeenv/issues/310>`_
-- Quoted values in the config file, as the README shows them, are read
-  without the quotes, and `user:password@` in the `--mirror` URL is sent to
+- Quoted values in the config file are read without the quotes, and
+  `user:password@` in the `--mirror` URL is sent to
   the mirror with HTTP Basic authentication instead of being taken for a part
   of the host; the password stays out of error messages and redirects
   `#321 <https://github.com/ekalinin/nodeenv/issues/321>`_
diff --git a/README.rst b/README.rst
index 21761eb..04a4f31 100644
--- a/README.rst
+++ b/README.rst
@@ -480,22 +480,25 @@ the keys in that file are the long command-line option names.
 These are the available options and their defaults::
 
     [nodeenv]
-    node = 'latest'
-    npm = 'latest'
+    node = latest
+    npm = latest
     with_npm = False
-    jobs = '2'
+    jobs = 2
     without_ssl = False
     debug = False
     profile = False
-    make = 'make'
+    make = make
     prebuilt = True
     ignore_ssl_certs = False
     with_certifi = False
-    mirror = None
     prefer_system = False
     isolate_npm = False
     clean_src = True
 
+Options without a default, such as ``mirror``, can be omitted. Do not use
+``mirror = None``: INI values are strings, so that would select a mirror
+named ``None`` instead of using nodeenv's default download source.
+
 Alternatives
 ------------
 
diff --git a/nodeenv.py b/nodeenv.py
index 7177ae1..644c97e 100644
--- a/nodeenv.py
+++ b/nodeenv.py
@@ -132,7 +132,7 @@ def _dump(cls):
         print("    [nodeenv]")
         print("    " + "\n    ".join(
             "%s = %s" % (k, v) for k, v in sorted(vars(cls).items())
-            if not k.startswith('_')))
+            if not k.startswith('_') and v is not None))
 
 
 Config._default = dict(
diff --git a/tests/test_config_dump.py b/tests/test_config_dump.py
new file mode 100644
index 0000000..10934df
--- /dev/null
+++ b/tests/test_config_dump.py
@@ -0,0 +1,34 @@
+import os
+import re
+
+import pytest
+
+import nodeenv
+
+
+@pytest.fixture
+def default_config(monkeypatch, tmpdir):
+    for name, value in nodeenv.Config._default.items():
+        monkeypatch.setattr(nodeenv.Config, name, value)
+    monkeypatch.chdir(str(tmpdir))
+
+
+def _load_defaults(text, tmpdir):
+    config = tmpdir.join('nodeenvrc')
+    config.write(text)
+    nodeenv.Config._load([str(config)])
+    assert {name: getattr(nodeenv.Config, name)
+            for name in nodeenv.Config._default} == nodeenv.Config._default
+
+
+def test_dumped_configuration_roundtrips(default_config, capsys, tmpdir):
+    nodeenv.Config._dump()
+    _load_defaults(capsys.readouterr().out, tmpdir)
+
+
+def test_readme_configuration_roundtrips(default_config, tmpdir):
+    readme = os.path.join(os.path.dirname(__file__), '..', 'README.rst')
+    with open(readme) as stream:
+        block = re.search(r'    \[nodeenv\]\n(?:    .*\n)+',
+                          stream.read()).group(0)
+    _load_defaults('\n'.join(line[4:] for line in block.splitlines()), tmpdir)