diff --git a/engineioxide/src/engine.rs b/engineioxide/src/engine.rs
index 1766b65d..d4e405fd 100644
--- a/engineioxide/src/engine.rs
+++ b/engineioxide/src/engine.rs
@@ -1,6 +1,8 @@
 #![deny(clippy::await_holding_lock)]
+
 use std::{
-    collections::HashMap,
+    collections::{hash_map::Entry, HashMap},
+    fmt::Debug,
     io::BufRead,
     sync::{Arc, RwLock},
 };
@@ -21,7 +23,6 @@ use bytes::Buf;
 use futures::{stream::SplitStream, SinkExt, StreamExt, TryStreamExt};
 use http::{Request, Response, StatusCode};
 use hyper::upgrade::Upgraded;
-use std::fmt::Debug;
 use tokio_tungstenite::{
     tungstenite::{protocol::Role, Message},
     WebSocketStream,
@@ -71,24 +72,31 @@ where
     {
         let engine = self.clone();
         let close_fn = Box::new(move |sid: Sid| engine.close_session(sid));
-        let sid = generate_sid();
-        let socket = Socket::new(
-            sid,
-            ConnectionType::Http,
-            &self.config,
-            SocketReq::from(req.into_parts().0),
-            close_fn,
-        );
-        let socket = Arc::new(socket);
-        {
-            self.sockets.write().unwrap().insert(sid, socket.clone());
-        }
+
+        let mut lock = self.sockets.write().unwrap();
+        let socket = loop {
+            let sid = generate_sid();
+            if let Entry::Vacant(entry) = lock.entry(sid) {
+                let socket = Socket::new(
+                    sid,
+                    ConnectionType::Http,
+                    &self.config,
+                    SocketReq::from(req.into_parts().0),
+                    close_fn,
+                );
+                let socket = Arc::new(socket);
+                entry.insert(socket.clone());
+                break socket;
+            }
+        };
+        drop(lock);
+
         socket
             .clone()
             .spawn_heartbeat(self.config.ping_interval, self.config.ping_timeout);
         self.handler.on_connect(&socket);
 
-        let packet = OpenPacket::new(TransportType::Polling, sid, &self.config);
+        let packet = OpenPacket::new(TransportType::Polling, socket.sid, &self.config);
         let packet: String = Packet::Open(packet).try_into()?;
         http_response(StatusCode::OK, packet).map_err(Error::Http)
     }
@@ -255,23 +263,31 @@ where
                 }
             }
         } else {
-            let sid = generate_sid();
             let engine = self.clone();
             let close_fn = Box::new(move |sid: Sid| engine.close_session(sid));
-            let socket = Socket::new(
-                sid,
-                ConnectionType::WebSocket,
-                &self.config,
-                req_data,
-                close_fn,
-            );
-            let socket = Arc::new(socket);
-            {
-                self.sockets.write().unwrap().insert(sid, socket.clone());
-            }
-            debug!("[sid={sid}] new websocket connection");
+
+            let socket = {
+                let mut lock = self.sockets.write().unwrap();
+                let socket = loop {
+                    let sid = generate_sid();
+                    if let Entry::Vacant(entry) = lock.entry(sid) {
+                        let socket = Socket::new(
+                            sid,
+                            ConnectionType::WebSocket,
+                            &self.config,
+                            req_data,
+                            close_fn,
+                        );
+                        let socket = Arc::new(socket);
+                        entry.insert(socket.clone());
+                        break socket;
+                    }
+                };
+                socket
+            };
+            debug!("[sid={}] new websocket connection", socket.sid);
             let mut ws = ws_init().await;
-            self.ws_init_handshake(sid, &mut ws).await?;
+            self.ws_init_handshake(socket.sid, &mut ws).await?;
             socket
                 .clone()
                 .spawn_heartbeat(self.config.ping_interval, self.config.ping_timeout);