diff --git a/radicale/__main__.py b/radicale/__main__.py
index d88aeeb..8f21ece 100644
--- a/radicale/__main__.py
+++ b/radicale/__main__.py
@@ -91,7 +91,7 @@ def run() -> None:
                 del kwargs["type"]
                 kwargs["action"] = "store_const"
                 kwargs["const"] = "True"
-                opposite_args = kwargs.pop("opposite", [])
+                opposite_args = list(kwargs.pop("opposite", ()))
                 opposite_args.append("--no%s" % long_name[1:])
                 group.add_argument(*args, **kwargs)
 
diff --git a/radicale/config.py b/radicale/config.py
index c094711..ec94ada 100644
--- a/radicale/config.py
+++ b/radicale/config.py
@@ -126,7 +126,7 @@ DEFAULT_CONFIG_SCHEMA: types.CONFIG_SCHEMA = OrderedDict([
             "value": "False",
             "help": "use SSL connection",
             "aliases": ("-s", "--ssl",),
-            "opposite": ["-S", "--no-ssl"],
+            "opposite": ("-S", "--no-ssl",),
             "type": bool}),
         ("certificate", {
             "value": "/etc/ssl/radicale.cert.pem",