diff --git a/setup_cfg_fmt.py b/setup_cfg_fmt.py
index 34e3824..afd3a45 100644
--- a/setup_cfg_fmt.py
+++ b/setup_cfg_fmt.py
@@ -75,6 +75,12 @@ TOX_TO_CLASSIFIERS = {
 }
 
 
+class NoTransformConfigParser(configparser.RawConfigParser):
+    def optionxform(self, s: str) -> str:
+        """disable default lower-casing"""
+        return s
+
+
 def _adjacent_filename(setup_cfg: str, filename: str) -> str:
     return os.path.join(os.path.dirname(setup_cfg), filename)
 
@@ -153,7 +159,7 @@ def _parse_python_requires(
 def _tox_envlist(setup_cfg: str) -> Generator[str, None, None]:
     tox_ini = _adjacent_filename(setup_cfg, 'tox.ini')
     if os.path.exists(tox_ini):
-        cfg = configparser.ConfigParser()
+        cfg = NoTransformConfigParser()
         cfg.read(tox_ini)
 
         envlist = cfg.get('tox', 'envlist', fallback='')
@@ -166,7 +172,7 @@ def _tox_envlist(setup_cfg: str) -> Generator[str, None, None]:
 def _python_requires(
         setup_cfg: str, *, min_py3_version: tuple[int, int],
 ) -> str | None:
-    cfg = configparser.ConfigParser()
+    cfg = NoTransformConfigParser()
     cfg.read(setup_cfg)
     current_value = cfg.get('options', 'python_requires', fallback='')
     classifiers = cfg.get('metadata', 'classifiers', fallback='')
@@ -207,7 +213,7 @@ def _python_requires(
 
 
 def _requires(
-        cfg: configparser.ConfigParser, which: str, section: str = 'options',
+        cfg: NoTransformConfigParser, which: str, section: str = 'options',
 ) -> list[str]:
     raw = cfg.get(section, which, fallback='')
 
@@ -356,7 +362,7 @@ def format_file(
     with open(filename) as f:
         contents = f.read()
 
-    cfg = configparser.ConfigParser()
+    cfg = NoTransformConfigParser()
     cfg.read_string(contents)
     _clean_sections(cfg)
 
@@ -467,7 +473,7 @@ def format_file(
     return new_contents != contents
 
 
-def _clean_sections(cfg: configparser.ConfigParser) -> None:
+def _clean_sections(cfg: NoTransformConfigParser) -> None:
     """Removes any empty options and sections."""
     for section in cfg.sections():
         new_options = {k: v for k, v in cfg[section].items() if v}

diff --git a/tests/setup_cfg_fmt_test.py b/tests/setup_cfg_fmt_test.py
index 0bc8310..b3372a7 100644
--- a/tests/setup_cfg_fmt_test.py
+++ b/tests/setup_cfg_fmt_test.py
@@ -951,6 +951,22 @@ def test_imp_classifiers_pypy_only(tmpdir):
     )
 
 
+def test_leaves_casing_of_unrelated_settings(tmpdir):
+    setup_cfg = tmpdir.join('setup.cfg')
+    setup_cfg.write(
+        '[metadata]\n'
+        'name = pkg\n'
+        'version = 1.0\n'
+        'classifiers =\n'
+        '    Programming Language :: Python :: Implementation :: CPython\n'
+        '\n'
+        '[tool:pytest]\n'
+        'DJANGO_SETTINGS_MODULE = test.test\n',
+    )
+
+    assert not main((str(setup_cfg),))
+
+
 def test_natural_sort():
     classifiers = [
         'Programming Language :: Python :: 3',

configparser is downcasing keys in unrelated sections
for instance this doesn't roundtrip:

```ini
[tool:pytest]
DJANGO_SETTINGS_MODULE = test.test
```
tests/setup_cfg_fmt_test.py::test_leaves_casing_of_unrelated_settings
tests/setup_cfg_fmt_test.py::test_ver_type_ok tests/setup_cfg_fmt_test.py::test_ver_type_error tests/setup_cfg_fmt_test.py::test_ver_type_not_a_version tests/setup_cfg_fmt_test.py::test_case_insensitive_glob[foo-[Ff][Oo][Oo]] tests/setup_cfg_fmt_test.py::test_case_insensitive_glob[FOO-[Ff][Oo][Oo]] tests/setup_cfg_fmt_test.py::test_case_insensitive_glob[licen[sc]e-[Ll][Ii][Cc][Ee][Nn][SsCc][Ee]] tests/setup_cfg_fmt_test.py::test_noop tests/setup_cfg_fmt_test.py::test_rewrite_requires[install_requires-normalizes tests/setup_cfg_fmt_test.py::test_rewrite_requires[setup_requires-normalizes tests/setup_cfg_fmt_test.py::test_rewrite[orders tests/setup_cfg_fmt_test.py::test_rewrite[normalizes tests/setup_cfg_fmt_test.py::test_rewrite[sorts tests/setup_cfg_fmt_test.py::test_rewrite[normalize tests/setup_cfg_fmt_test.py::test_normalize_lib[no tests/setup_cfg_fmt_test.py::test_normalize_lib[whitespace tests/setup_cfg_fmt_test.py::test_normalize_lib[<= tests/setup_cfg_fmt_test.py::test_normalize_lib[>= tests/setup_cfg_fmt_test.py::test_normalize_lib[b/w tests/setup_cfg_fmt_test.py::test_normalize_lib[compatible tests/setup_cfg_fmt_test.py::test_adds_long_description_with_readme[README.rst-text/x-rst] tests/setup_cfg_fmt_test.py::test_adds_long_description_with_readme[README.markdown-text/markdown] tests/setup_cfg_fmt_test.py::test_adds_long_description_with_readme[README.md-text/markdown] tests/setup_cfg_fmt_test.py::test_adds_long_description_with_readme[README-text/plain] tests/setup_cfg_fmt_test.py::test_adds_long_description_with_readme[readme.txt-text/plain] tests/setup_cfg_fmt_test.py::test_readme_discover_prefers_file_over_directory tests/setup_cfg_fmt_test.py::test_sets_license_file_if_license_exists[LICENSE] tests/setup_cfg_fmt_test.py::test_sets_license_file_if_license_exists[LICENCE] tests/setup_cfg_fmt_test.py::test_sets_license_file_if_license_exists[LICENSE.md] tests/setup_cfg_fmt_test.py::test_sets_license_file_if_license_exists[license.txt] tests/setup_cfg_fmt_test.py::test_license_does_not_match_directories tests/setup_cfg_fmt_test.py::test_rewrite_sets_license_type_and_classifier tests/setup_cfg_fmt_test.py::test_rewrite_identifies_license tests/setup_cfg_fmt_test.py::test_python_requires_left_alone[already tests/setup_cfg_fmt_test.py::test_python_requires_left_alone[weird tests/setup_cfg_fmt_test.py::test_python_requires_left_alone[not tests/setup_cfg_fmt_test.py::test_strips_empty_options_and_sections[only tests/setup_cfg_fmt_test.py::test_strips_empty_options_and_sections[entire tests/setup_cfg_fmt_test.py::test_guess_python_requires_python2_tox_ini tests/setup_cfg_fmt_test.py::test_guess_python_requires_tox_ini_dashed_name tests/setup_cfg_fmt_test.py::test_guess_python_requires_ignores_insufficient_version_envs tests/setup_cfg_fmt_test.py::test_guess_python_requires_from_classifiers tests/setup_cfg_fmt_test.py::test_min_py3_version_updates_python_requires tests/setup_cfg_fmt_test.py::test_min_py3_version_greater_than_minimum tests/setup_cfg_fmt_test.py::test_min_version_removes_classifiers tests/setup_cfg_fmt_test.py::test_python_requires_with_patch_version tests/setup_cfg_fmt_test.py::test_classifiers_left_alone_for_odd_python_requires tests/setup_cfg_fmt_test.py::test_min_py3_version_less_than_minimum tests/setup_cfg_fmt_test.py::test_rewrite_extras tests/setup_cfg_fmt_test.py::test_imp_classifiers_from_tox_ini tests/setup_cfg_fmt_test.py::test_imp_classifiers_no_change tests/setup_cfg_fmt_test.py::test_imp_classifiers_pypy_only tests/setup_cfg_fmt_test.py::test_natural_sort