diff --git a/tests/test_cli.py b/tests/test_cli.py
index 40dc72fab1..cf0ec046b4 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -728,15 +728,18 @@ def test_shell_plus(
         (['convert', '.']),
         (['convert', '.tmuxp.yaml']),
         (['convert', '.tmuxp.yaml', '-y']),
+        (['convert', '.tmuxp.yml']),
+        (['convert', '.tmuxp.yml', '-y']),
     ],
 )
 def test_convert(cli_args, tmpdir, monkeypatch):
     # create dummy tmuxp yaml so we don't get yelled at
-    tmpdir.join('.tmuxp.yaml').write(
-        """
-session_name: hello
-    """
-    )
+    filename = cli_args[1]
+    if filename == '.':
+        filename = '.tmuxp.yaml'
+    file_ext = filename.rsplit('.', 1)[-1]
+    assert file_ext in ['yaml', 'yml'], file_ext
+    tmpdir.join(filename).write('\nsession_name: hello\n')
     tmpdir.join('.oh-my-zsh').ensure(dir=True)
     monkeypatch.setenv('HOME', str(tmpdir))
 
@@ -753,6 +756,31 @@ def test_convert(cli_args, tmpdir, monkeypatch):
         )
 
 
+@pytest.mark.parametrize(
+    "cli_args",
+    [
+        (['convert', '.']),
+        (['convert', '.tmuxp.json']),
+        (['convert', '.tmuxp.json', '-y']),
+    ],
+)
+def test_convert_json(cli_args, tmpdir, monkeypatch):
+    # create dummy tmuxp yaml so we don't get yelled at
+    tmpdir.join('.tmuxp.json').write('{"session_name": "hello"}')
+    tmpdir.join('.oh-my-zsh').ensure(dir=True)
+    monkeypatch.setenv('HOME', str(tmpdir))
+
+    with tmpdir.as_cwd():
+        runner = CliRunner()
+
+        # If autoconfirm (-y) no need to prompt y
+        input_args = 'y\ny\n' if '-y' not in cli_args else ''
+
+        runner.invoke(cli.cli, cli_args, input=input_args)
+        assert tmpdir.join('.tmuxp.yaml').check()
+        assert tmpdir.join('.tmuxp.yaml').open().read() == 'session_name: hello\n'
+
+
 @pytest.mark.parametrize("cli_args", [(['import'])])
 def test_import(cli_args, monkeypatch):
     runner = CliRunner()
diff --git a/tmuxp/cli.py b/tmuxp/cli.py
index 811086698d..201d72282e 100644
--- a/tmuxp/cli.py
+++ b/tmuxp/cli.py
@@ -1186,10 +1186,15 @@ def command_convert(confirmed, config):
     """Convert a tmuxp config between JSON and YAML."""
 
     _, ext = os.path.splitext(config)
-    if 'json' in ext:
+    ext = ext.lower()
+    if ext == '.json':
         to_filetype = 'yaml'
-    elif 'yaml' in ext:
+    elif ext in ['.yaml', '.yml']:
         to_filetype = 'json'
+    else:
+        raise click.BadParameter(
+            'Unknown filetype: %s (valid: [.json, .yaml, .yml])' % (ext,)
+        )
 
     configparser = kaptan.Kaptan()
     configparser.import_config(config)