diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ceb70a..7cab500 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ## Version 0.4.1 (development)
 
 - Latest updates from PyScaffold
+- Fix issue with kebab-cased-keys in `setup.cfg`, PR #13
 
 ## Version 0.4
 
diff --git a/src/pyscaffoldext/markdown/extension.py b/src/pyscaffoldext/markdown/extension.py
index 39340aa..e788fcc 100644
--- a/src/pyscaffoldext/markdown/extension.py
+++ b/src/pyscaffoldext/markdown/extension.py
@@ -8,6 +8,7 @@
 from pyscaffold import file_system as fs
 from pyscaffold.actions import Action, ActionParams, ScaffoldOpts, Structure
 from pyscaffold.extensions import Extension
+from pyscaffold.identification import dasherize
 from pyscaffold.log import logger
 from pyscaffold.operations import FileContents, FileOp, no_overwrite
 from pyscaffold.structure import merge, reify_leaf, reject
@@ -19,6 +20,8 @@
 __copyright__ = "Florian Wilhelm"
 __license__ = "MIT"
 
+DESC_KEY = "long_description"
+TYPE_KEY = "long_description_content_type"
 
 DOC_REQUIREMENTS = ["recommonmark"]
 
@@ -38,13 +41,19 @@ def add_long_desc(content: str) -> str:
     updater = ConfigUpdater()
     updater.read_string(content)
     metadata = updater["metadata"]
-    metadata["long-description"].value = "file: README.md"
-    long_desc_type = "long-description-content-type"
+
+    long_desc = metadata.get(dasherize(DESC_KEY)) or metadata.get(DESC_KEY)
+    long_desc.key = DESC_KEY  # dash-separated keys are deprecated in setuptools
+    long_desc.value = "file: README.md"
     long_desc_value = "text/markdown; charset=UTF-8; variant=GFM"
-    if long_desc_type not in metadata:
-        metadata["long-description"].add_after.option(long_desc_type, long_desc_value)
+
+    long_desc_type = metadata.get(dasherize(TYPE_KEY)) or metadata.get(TYPE_KEY)
+    if long_desc_type:
+        long_desc_type.key = TYPE_KEY
+        long_desc_type.value = long_desc_value
     else:
-        metadata[long_desc_type].value = long_desc_value
+        long_desc.add_after.option(TYPE_KEY, long_desc_value)
+
     return str(updater)
 
 
diff --git a/tests/test_markdown.py b/tests/test_markdown.py
index 8c40c55..71fc1d5 100644
--- a/tests/test_markdown.py
+++ b/tests/test_markdown.py
@@ -1,10 +1,11 @@
 from configparser import ConfigParser
+from textwrap import dedent
 
 import pytest
 from pyscaffold import __version__ as pyscaffold_version
 from pyscaffold import api, cli
 
-from pyscaffoldext.markdown.extension import DOC_REQUIREMENTS, Markdown
+from pyscaffoldext.markdown.extension import DOC_REQUIREMENTS, Markdown, add_long_desc
 
 CONV_FILES = [
     "README",
@@ -17,6 +18,42 @@
 ]
 
 
+def test_underscore_keys():
+    # Dash-separated keys for setup.cfg were deprecated by setuptools, so it is good to
+    # ensure they don't occur
+    examples = [
+        """\
+        [metadata]
+        long-description: a-pkg
+        long-description-content-type: text/x-rst
+        """,
+        """\
+        [metadata]
+        long_description: a-pkg
+        long_description_content_type: text/x-rst
+        """,
+        """\
+        [metadata]
+        long-description: a-pkg
+        """,
+        """\
+        [metadata]
+        long_description: a-pkg
+        """,
+    ]
+
+    for example in examples:
+        modified = add_long_desc(dedent(example))
+        cfg = ConfigParser()
+        cfg.read_string(modified)
+        options = list(cfg["metadata"].keys())
+        print(modified)
+        assert "long_description" in options
+        assert "long_description_content_type" in options
+        assert "long-description" not in options
+        assert "long-description-content-type" not in options
+
+
 @pytest.mark.slow
 def test_create_project_with_markdown(tmpfolder):
     # Given options with the markdown extension,
@@ -42,7 +79,8 @@ def test_create_project_with_markdown(tmpfolder):
     existing_setup = (tmpfolder / "proj/setup.cfg").read_text()
     cfg = ConfigParser()
     cfg.read_string(existing_setup)
-    assert "text/markdown" in str(cfg["metadata"]["long-description-content-type"])
+    assert "text/markdown" in str(cfg["metadata"]["long_description_content_type"])
+    assert "file: README" in str(cfg["metadata"]["long_description"])
 
     # and new doc requirements should be added to docs/requirements.txt
     requirements_txt = (tmpfolder / "proj/docs/requirements.txt").read_text()