diff --git a/tcp_relay_server/src/args.rs b/tcp_relay_server/src/args.rs
index 9f80c24..7b24fce 100644
--- a/tcp_relay_server/src/args.rs
+++ b/tcp_relay_server/src/args.rs
@@ -12,6 +12,10 @@ pub struct Args {
     #[clap(short, long)]
     pub ports: Vec<u16>,
 
+    /// Upstream server
+    #[clap(short, long, default_value = "127.0.0.1")]
+    pub upstream_server: String,
+
     /// HTTP server listen address
     #[clap(short, long, default_value = "0.0.0.0:8000")]
     pub listen_address: String,