diff --git a/electrum/plugins/payserver/__init__.py b/electrum/plugins/payserver/__init__.py
index 9e10d3f76..28f930788 100644
--- a/electrum/plugins/payserver/__init__.py
+++ b/electrum/plugins/payserver/__init__.py
@@ -1,5 +1,5 @@
 from electrum.simple_config import ConfigVar, SimpleConfig
 
-SimpleConfig.PAYSERVER_PORT = ConfigVar('payserver_port', default=8080, type_=int)
-SimpleConfig.PAYSERVER_ROOT = ConfigVar('payserver_root', default='/r', type_=str)
-SimpleConfig.PAYSERVER_ALLOW_CREATE_INVOICE = ConfigVar('payserver_allow_create_invoice', default=False, type_=bool)
+SimpleConfig.PAYSERVER_PORT = ConfigVar('payserver_port', default=8080, type_=int, plugin=__name__)
+SimpleConfig.PAYSERVER_ROOT = ConfigVar('payserver_root', default='/r', type_=str, plugin=__name__)
+SimpleConfig.PAYSERVER_ALLOW_CREATE_INVOICE = ConfigVar('payserver_allow_create_invoice', default=False, type_=bool, plugin=__name__)
diff --git a/electrum/plugins/swapserver/__init__.py b/electrum/plugins/swapserver/__init__.py
index 0aeeb4629..f5a98487f 100644
--- a/electrum/plugins/swapserver/__init__.py
+++ b/electrum/plugins/swapserver/__init__.py
@@ -1,5 +1,5 @@
 from electrum.simple_config import ConfigVar, SimpleConfig
 
-SimpleConfig.SWAPSERVER_PORT = ConfigVar('swapserver_port', default=None, type_=int)
-SimpleConfig.SWAPSERVER_FEE_MILLIONTHS = ConfigVar('swapserver_fee_millionths', default=5000, type_=int)
-SimpleConfig.SWAPSERVER_ANN_POW_NONCE = ConfigVar('swapserver_ann_pow_nonce', default=0, type_=int)
+SimpleConfig.SWAPSERVER_PORT = ConfigVar('swapserver_port', default=None, type_=int, plugin=__name__)
+SimpleConfig.SWAPSERVER_FEE_MILLIONTHS = ConfigVar('swapserver_fee_millionths', default=5000, type_=int, plugin=__name__)
+SimpleConfig.SWAPSERVER_ANN_POW_NONCE = ConfigVar('swapserver_ann_pow_nonce', default=0, type_=int, plugin=__name__)
diff --git a/electrum/plugins/watchtower/__init__.py b/electrum/plugins/watchtower/__init__.py
index 35384fbdc..b4d66af1e 100644
--- a/electrum/plugins/watchtower/__init__.py
+++ b/electrum/plugins/watchtower/__init__.py
@@ -1,5 +1,5 @@
 from electrum.simple_config import ConfigVar, SimpleConfig
 
-SimpleConfig.WATCHTOWER_SERVER_PORT = ConfigVar('watchtower_server_port', default=None, type_=int)
-SimpleConfig.WATCHTOWER_SERVER_USER = ConfigVar('watchtower_server_user', default=None, type_=str)
-SimpleConfig.WATCHTOWER_SERVER_PASSWORD = ConfigVar('watchtower_server_password', default=None, type_=str)
+SimpleConfig.WATCHTOWER_SERVER_PORT = ConfigVar('watchtower_server_port', default=None, type_=int, plugin=__name__)
+SimpleConfig.WATCHTOWER_SERVER_USER = ConfigVar('watchtower_server_user', default=None, type_=str, plugin=__name__)
+SimpleConfig.WATCHTOWER_SERVER_PASSWORD = ConfigVar('watchtower_server_password', default=None, type_=str, plugin=__name__)
diff --git a/electrum/simple_config.py b/electrum/simple_config.py
index dfbc5ff82..ed3b2eff3 100644
--- a/electrum/simple_config.py
+++ b/electrum/simple_config.py
@@ -45,6 +45,7 @@ class ConfigVar(property):
         convert_getter: Callable[[Any], Any] = None,
         short_desc: Callable[[], str] = None,
         long_desc: Callable[[], str] = None,
+        plugin: Optional[str] = None,
     ):
         self._key = key
         self._default = default
@@ -56,6 +57,13 @@ class ConfigVar(property):
         assert long_desc is None or callable(long_desc)
         self._short_desc = short_desc
         self._long_desc = long_desc
+        if plugin:  # enforce "key" starts with name of plugin
+            pkg_prefix = "electrum.plugins."  # for internal plugins
+            if plugin.startswith(pkg_prefix):
+                plugin = plugin[len(pkg_prefix):]
+            assert "." not in plugin, plugin
+            key_prefix = plugin + "_"
+            assert key.startswith(key_prefix), f"ConfigVar {key=} must be prefixed with the plugin name ({key_prefix})"
         property.__init__(self, self._get_config_value, self._set_config_value)
         assert key not in _config_var_from_key, f"duplicate config key str: {key!r}"
         _config_var_from_key[key] = self