diff --git a/app/src/Room.js b/app/src/Room.js
index 102991c0..6249372c 100644
--- a/app/src/Room.js
+++ b/app/src/Room.js
@@ -108,6 +108,10 @@ module.exports = class Room {
         return this.peers;
     }
 
+    getPeersCount() {
+        return this.peers.size;
+    }
+
     toJson() {
         return {
             id: this.id,
diff --git a/app/src/Server.js b/app/src/Server.js
index da040c83..ba578032 100644
--- a/app/src/Server.js
+++ b/app/src/Server.js
@@ -469,6 +469,16 @@ io.on('connection', (socket) => {
         }
     });
 
+    socket.on('getPeerCounts', async ({}, callback) => {
+        if (!roomList.has(socket.room_id)) return;
+
+        let peerCounts = roomList.get(socket.room_id).getPeersCount();
+
+        log.debug('Peer counts', { peerCounts: peerCounts });
+
+        callback({ peerCounts: peerCounts });
+    });
+
     socket.on('roomAction', (data) => {
         if (!roomList.has(socket.room_id)) return;
 
diff --git a/public/js/RoomClient.js b/public/js/RoomClient.js
index 67844cad..ed25fa73 100644
--- a/public/js/RoomClient.js
+++ b/public/js/RoomClient.js
@@ -3193,9 +3193,22 @@ class RoomClient {
             switch (action) {
                 case 'lock':
                     if (room_password) {
-                        data.password = room_password;
-                        this.socket.emit('roomAction', data);
-                        this.roomStatus(action);
+                        this.socket
+                            .request('getPeerCounts')
+                            .then(
+                                async function (data) {
+                                    // Only the presenter can lock the room
+                                    if (isPresenter || data.peerCounts == 1) {
+                                        isPresenter = true;
+                                        data.password = room_password;
+                                        this.socket.emit('roomAction', data);
+                                        this.roomStatus(action);
+                                    }
+                                }.bind(this),
+                            )
+                            .catch((err) => {
+                                console.log('Get peer counts:', err);
+                            });
                     } else {
                         Swal.fire({
                             allowOutsideClick: false,