diff --git a/lib/socket.ts b/lib/socket.ts
index c14b9d4fc7..541e15f58b 100644
--- a/lib/socket.ts
+++ b/lib/socket.ts
@@ -71,7 +71,6 @@ export class Socket extends EventEmitter {
   public readonly id: SocketId;
   public readonly handshake: Handshake;
 
-  public rooms = {};
   public connected: boolean;
   public disconnected: boolean;
 
@@ -242,24 +241,14 @@ export class Socket extends EventEmitter {
    * @param {Function} fn - optional, callback
    * @return {Socket} self
    */
-  public join(rooms, fn?: (err: Error) => void): Socket {
+  public join(rooms: Room | Array<Room>, fn?: (err: Error) => void): Socket {
     debug("joining room %s", rooms);
 
-    if (!Array.isArray(rooms)) {
-      rooms = [rooms];
-    }
-    rooms = rooms.filter(room => {
-      return !this.rooms.hasOwnProperty(room);
-    });
-    if (!rooms.length) {
-      fn && fn(null);
-      return this;
-    }
-    this.adapter.addAll(this.id, rooms);
+    this.adapter.addAll(
+      this.id,
+      new Set(Array.isArray(rooms) ? rooms : [rooms])
+    );
     debug("joined room %s", rooms);
-    rooms.forEach(room => {
-      this.rooms[room] = room;
-    });
     fn && fn(null);
     return this;
   }
@@ -276,7 +265,6 @@ export class Socket extends EventEmitter {
     this.adapter.del(this.id, room);
 
     debug("left room %s", room);
-    delete this.rooms[room];
     fn && fn(null);
 
     return this;
@@ -287,7 +275,6 @@ export class Socket extends EventEmitter {
    */
   private leaveAll(): void {
     this.adapter.delAll(this.id);
-    this.rooms = {};
   }
 
   /**
@@ -584,4 +571,8 @@ export class Socket extends EventEmitter {
   public get conn() {
     return this.client.conn;
   }
+
+  public get rooms(): Set<Room> {
+    return this.adapter.socketRooms(this.id) || new Set();
+  }
 }
diff --git a/test/socket.io.js b/test/socket.io.js
index 216ae7bed3..2edbdb40ed 100644
--- a/test/socket.io.js
+++ b/test/socket.io.js
@@ -682,12 +682,12 @@ describe("socket.io", () => {
 
           let total = 2;
           s.on("disconnecting", reason => {
-            expect(Object.keys(s.rooms)).to.eql([s.id, "a"]);
+            expect(s.rooms).to.contain(s.id, "a");
             total--;
           });
 
           s.on("disconnect", reason => {
-            expect(Object.keys(s.rooms)).to.eql([]);
+            expect(s.rooms.size).to.eql(0);
             --total || done();
           });
         });
@@ -2150,15 +2150,15 @@ describe("socket.io", () => {
         const socket = client(srv);
         sio.on("connection", s => {
           s.join("a", () => {
-            expect(Object.keys(s.rooms)).to.eql([s.id, "a"]);
+            expect(s.rooms).to.contain(s.id, "a");
             s.join("b", () => {
-              expect(Object.keys(s.rooms)).to.eql([s.id, "a", "b"]);
+              expect(s.rooms).to.contain(s.id, "a", "b");
               s.join("c", () => {
-                expect(Object.keys(s.rooms)).to.eql([s.id, "a", "b", "c"]);
+                expect(s.rooms).to.contain(s.id, "a", "b", "c");
                 s.leave("b", () => {
-                  expect(Object.keys(s.rooms)).to.eql([s.id, "a", "c"]);
+                  expect(s.rooms).to.contain(s.id, "a", "c");
                   s.leaveAll();
-                  expect(Object.keys(s.rooms)).to.eql([]);
+                  expect(s.rooms.size).to.eql(0);
                   done();
                 });
               });
@@ -2194,13 +2194,13 @@ describe("socket.io", () => {
         const socket = client(srv);
         sio.on("connection", s => {
           s.join("a", () => {
-            expect(Object.keys(s.rooms)).to.eql([s.id, "a"]);
+            expect(s.rooms).to.contain(s.id, "a");
             s.join("b", () => {
-              expect(Object.keys(s.rooms)).to.eql([s.id, "a", "b"]);
+              expect(s.rooms).to.contain(s.id, "a", "b");
               s.leave("unknown", () => {
-                expect(Object.keys(s.rooms)).to.eql([s.id, "a", "b"]);
+                expect(s.rooms).to.contain(s.id, "a", "b");
                 s.leaveAll();
-                expect(Object.keys(s.rooms)).to.eql([]);
+                expect(s.rooms.size).to.eql(0);
                 done();
               });
             });
@@ -2217,7 +2217,7 @@ describe("socket.io", () => {
         const socket = client(srv);
         sio.on("connection", s => {
           s.join(["a", "b", "c"], () => {
-            expect(Object.keys(s.rooms)).to.eql([s.id, "a", "b", "c"]);
+            expect(s.rooms).to.contain(s.id, "a", "b", "c");
             done();
           });
         });