diff --git a/datasette/publish/heroku.py b/datasette/publish/heroku.py
index 2b8977f1..f576a346 100644
--- a/datasette/publish/heroku.py
+++ b/datasette/publish/heroku.py
@@ -194,7 +194,7 @@ def temporary_heroku_directory(
                 fp.write(json.dumps(metadata_content, indent=2))
 
         with open("runtime.txt", "w") as fp:
-            fp.write("python-3.8.10")
+            fp.write("python-3.11.0")
 
         if branch:
             install = [
diff --git a/tests/test_publish_heroku.py b/tests/test_publish_heroku.py
index faab340e..cab83654 100644
--- a/tests/test_publish_heroku.py
+++ b/tests/test_publish_heroku.py
@@ -133,8 +133,15 @@ def test_publish_heroku_plugin_secrets(
 
 @pytest.mark.serial
 @mock.patch("shutil.which")
-def test_publish_heroku_generate_dir(mock_which, tmp_path_factory):
+@mock.patch("datasette.publish.heroku.check_output")
+@mock.patch("datasette.publish.heroku.call")
+def test_publish_heroku_generate_dir(
+    mock_call, mock_check_output, mock_which, tmp_path_factory
+):
     mock_which.return_value = True
+    mock_check_output.side_effect = lambda s: {
+        "['heroku', 'plugins']": b"heroku-builds",
+    }[repr(s)]
     runner = CliRunner()
     os.chdir(tmp_path_factory.mktemp("runner"))
     with open("test.db", "w") as fp:
@@ -163,7 +170,7 @@ def test_publish_heroku_generate_dir(mock_which, tmp_path_factory):
     }
     for name, expected in (
         ("requirements.txt", "datasette"),
-        ("runtime.txt", "python-3.8.10"),
+        ("runtime.txt", "python-3.11.0"),
         (
             "Procfile",
             (