diff --git a/lib/provider/CustomProvider.ts b/lib/provider/CustomProvider.ts
index 11e7275df..496ae1453 100644
--- a/lib/provider/CustomProvider.ts
+++ b/lib/provider/CustomProvider.ts
@@ -18,6 +18,7 @@ export default class CustomProvider extends Provider {
       mptcp: Joi.boolean().strict(),
       binPath: Joi.string(),
       localPort: Joi.number(),
+      'underlying-proxy': Joi.string(),
     })
       .unknown();
     const schema = Joi.object({
diff --git a/lib/utils/index.ts b/lib/utils/index.ts
index 3b0b74232..370782f29 100644
--- a/lib/utils/index.ts
+++ b/lib/utils/index.ts
@@ -193,7 +193,7 @@ export const getSurgeNodes = function(
             ].join(' = '));
           }
 
-          // Using external provider
+          // Using custom format
           return ([
             config.nodeName,
             [