diff --git a/src/peer.rs b/src/peer.rs
index 0f218df..9e4cbec 100644
--- a/src/peer.rs
+++ b/src/peer.rs
@@ -22,6 +22,9 @@ pub const IP_CHANGE_DUR: u64 = 180;
 pub const IP_CHANGE_DUR_X2: u64 = IP_CHANGE_DUR * 2;
 pub const DAY_SECONDS: u64 = 3600 * 24;
 pub const IP_BLOCK_DUR: u64 = 60;
+// Same bound as the Pro server: a longer id is not a normal RustDesk id or hostname,
+// and every peer entry and punch-request record keeps its own copy.
+pub const MAX_PEER_ID_LEN: usize = 253;
 
 #[derive(Debug, Default, Serialize, Deserialize, Clone)]
 pub(crate) struct PeerInfo {
diff --git a/src/rendezvous_server.rs b/src/rendezvous_server.rs
index 57bc5b8..54d24a2 100644
--- a/src/rendezvous_server.rs
+++ b/src/rendezvous_server.rs
@@ -373,7 +373,7 @@ impl RendezvousServer {
             match msg_in.union {
                 Some(rendezvous_message::Union::RegisterPeer(rp)) => {
                     // B registered
-                    if !rp.id.is_empty() {
+                    if !rp.id.is_empty() && rp.id.len() <= MAX_PEER_ID_LEN {
                         log::trace!("New peer registered: {:?} {:?}", &rp.id, &addr);
                         self.update_addr(rp.id, addr, socket).await?;
                         if self.inner.serial > rp.serial {
@@ -393,7 +393,7 @@ impl RendezvousServer {
                     }
                     let id = rk.id;
                     let ip = addr.ip().to_string();
-                    if id.len() < 6 {
+                    if id.len() < 6 || id.len() > MAX_PEER_ID_LEN {
                         return send_rk_res(socket, addr, UUID_MISMATCH).await;
                     } else if !self.check_ip_blocker(&ip, &id).await {
                         return send_rk_res(socket, addr, TOO_FREQUENT).await;