diff --git a/packages/socket.io-adapter/lib/in-memory-adapter.ts b/packages/socket.io-adapter/lib/in-memory-adapter.ts
index cf178170e0..e39a9d1bf5 100644
--- a/packages/socket.io-adapter/lib/in-memory-adapter.ts
+++ b/packages/socket.io-adapter/lib/in-memory-adapter.ts
@@ -214,12 +214,14 @@ export class Adapter extends EventEmitter {
     const encodedPackets = this._encode(packet, packetOpts);
 
     let clientCount = 0;
+    const sockets: any[] = [];
 
     this.apply(opts, (socket) => {
       // track the total number of acknowledgements that are expected
       clientCount++;
       // call the ack callback for each client response
       socket.acks.set(packet.id, ack);
+      sockets.push(socket);
 
       if (typeof socket.notifyOutgoingListeners === "function") {
         socket.notifyOutgoingListeners(packet);
@@ -229,6 +231,16 @@ export class Adapter extends EventEmitter {
     });
 
     clientCountCallback(clientCount);
+
+    // clean up socket.acks entries after the timeout to prevent memory leaks
+    // when clients do not respond with an acknowledgement
+    if (flags.timeout !== undefined) {
+      setTimeout(() => {
+        for (const socket of sockets) {
+          socket.acks.delete(packet.id);
+        }
+      }, flags.timeout);
+    }
   }
 
   private _encode(packet: unknown, packetOpts: Record<string, unknown>) {
diff --git a/packages/socket.io-adapter/test/index.ts b/packages/socket.io-adapter/test/index.ts
index 285ae66f02..9895c0bc3b 100644
--- a/packages/socket.io-adapter/test/index.ts
+++ b/packages/socket.io-adapter/test/index.ts
@@ -317,6 +317,120 @@ describe("socket.io-adapter", () => {
     });
   });
 
+  describe("broadcastWithAck", () => {
+    it("should clean up socket.acks after timeout", (done) => {
+      const acks1 = new Map();
+      const acks2 = new Map();
+      let _ids = 0;
+
+      function socket(id, acks) {
+        return [
+          id,
+          {
+            id,
+            acks,
+            client: {
+              writeToEngine() {},
+            },
+          },
+        ];
+      }
+
+      const nsp = {
+        _ids,
+        name: "/",
+        server: {
+          encoder: {
+            encode() {
+              return ["123"];
+            },
+          },
+        },
+        // @ts-ignore
+        sockets: new Map([socket("s1", acks1), socket("s2", acks2)]),
+      };
+
+      const adapter = new Adapter(nsp);
+      adapter.addAll("s1", new Set(["r1"]));
+      adapter.addAll("s2", new Set(["r1"]));
+
+      const ackFn = () => {};
+
+      adapter.broadcastWithAck(
+        { type: 2, data: ["test", ackFn] },
+        {
+          rooms: new Set(["r1"]),
+          except: new Set(),
+          flags: { timeout: 50 },
+        },
+        () => {},
+        ackFn,
+      );
+
+      // acks should be set immediately
+      expect(acks1.size).to.be(1);
+      expect(acks2.size).to.be(1);
+
+      // acks should be cleaned up after timeout
+      setTimeout(() => {
+        expect(acks1.size).to.be(0);
+        expect(acks2.size).to.be(0);
+        done();
+      }, 100);
+    });
+
+    it("should not set cleanup timer when no timeout is specified", () => {
+      const acks1 = new Map();
+      let _ids = 0;
+
+      function socket(id, acks) {
+        return [
+          id,
+          {
+            id,
+            acks,
+            client: {
+              writeToEngine() {},
+            },
+          },
+        ];
+      }
+
+      const nsp = {
+        _ids,
+        name: "/",
+        server: {
+          encoder: {
+            encode() {
+              return ["123"];
+            },
+          },
+        },
+        // @ts-ignore
+        sockets: new Map([socket("s1", acks1)]),
+      };
+
+      const adapter = new Adapter(nsp);
+      adapter.addAll("s1", new Set(["r1"]));
+
+      const ackFn = () => {};
+
+      adapter.broadcastWithAck(
+        { type: 2, data: ["test", ackFn] },
+        {
+          rooms: new Set(["r1"]),
+          except: new Set(),
+          flags: {},
+        },
+        () => {},
+        ackFn,
+      );
+
+      // acks should be set
+      expect(acks1.size).to.be(1);
+    });
+  });
+
   describe("connection state recovery", () => {
     it("should persist and restore session", async () => {
       const adapter = new SessionAwareAdapter({