diff --git a/.swift-version b/.swift-version
index 4d54dad..bec3a35 100644
--- a/.swift-version
+++ b/.swift-version
@@ -1 +1 @@
-4.0.2
+system
diff --git a/Source/SocketIO/Ack/SocketAckEmitter.swift b/Source/SocketIO/Ack/SocketAckEmitter.swift
index 449d04e..a7c80be 100644
--- a/Source/SocketIO/Ack/SocketAckEmitter.swift
+++ b/Source/SocketIO/Ack/SocketAckEmitter.swift
@@ -121,9 +121,9 @@ public final class OnAckCallback : NSObject {
         guard seconds != 0 else { return }
 
         socket.manager?.handleQueue.asyncAfter(deadline: DispatchTime.now() + seconds) {[weak socket] in
-            guard let socket = socket, let manager = socket.manager else { return }
+            guard let socket = socket else { return }
 
-            socket.ackHandlers.timeoutAck(self.ackNumber, onQueue: manager.handleQueue)
+            socket.ackHandlers.timeoutAck(self.ackNumber)
         }
     }
 
diff --git a/Source/SocketIO/Ack/SocketAckManager.swift b/Source/SocketIO/Ack/SocketAckManager.swift
index cda3271..21fb009 100644
--- a/Source/SocketIO/Ack/SocketAckManager.swift
+++ b/Source/SocketIO/Ack/SocketAckManager.swift
@@ -60,29 +60,18 @@ private struct SocketAck : Hashable {
 
 struct SocketAckManager {
     private var acks = Set<SocketAck>(minimumCapacity: 1)
-    private let ackSemaphore = DispatchSemaphore(value: 1)
 
     mutating func addAck(_ ack: Int, callback: @escaping AckCallback) {
         acks.insert(SocketAck(ack: ack, callback: callback))
     }
 
     /// Should be called on handle queue
-    mutating func executeAck(_ ack: Int, with items: [Any], onQueue: DispatchQueue) {
-        ackSemaphore.wait()
-        defer { ackSemaphore.signal() }
-        let ack = acks.remove(SocketAck(ack: ack))
-
-        onQueue.async() { ack?.callback(items) }
+    mutating func executeAck(_ ack: Int, with items: [Any]) {
+        acks.remove(SocketAck(ack: ack))?.callback(items)
     }
 
     /// Should be called on handle queue
-    mutating func timeoutAck(_ ack: Int, onQueue: DispatchQueue) {
-        ackSemaphore.wait()
-        defer { ackSemaphore.signal() }
-        let ack = acks.remove(SocketAck(ack: ack))
-
-        onQueue.async() {
-            ack?.callback?([SocketAckStatus.noAck.rawValue])
-        }
+    mutating func timeoutAck(_ ack: Int) {
+       acks.remove(SocketAck(ack: ack))?.callback?([SocketAckStatus.noAck.rawValue])
     }
 }
diff --git a/Source/SocketIO/Client/SocketIOClient.swift b/Source/SocketIO/Client/SocketIOClient.swift
index b6515e6..76544b9 100644
--- a/Source/SocketIO/Client/SocketIOClient.swift
+++ b/Source/SocketIO/Client/SocketIOClient.swift
@@ -314,11 +314,11 @@ open class SocketIOClient : NSObject, SocketIOClientSpec {
     /// - parameter data: The data sent back with this ack.
     @objc
     open func handleAck(_ ack: Int, data: [Any]) {
-        guard status == .connected, let manager = self.manager else { return }
+        guard status == .connected else { return }
 
         DefaultSocketLogger.Logger.log("Handling ack: \(ack) with data: \(data)", type: logType)
 
-        ackHandlers.executeAck(ack, with: data, onQueue: manager.handleQueue)
+        ackHandlers.executeAck(ack, with: data)
     }
 
     /// Called on socket.io specific events.
diff --git a/Tests/TestSocketIO/SocketAckManagerTest.swift b/Tests/TestSocketIO/SocketAckManagerTest.swift
index 455c5b9..b4f7b5d 100644
--- a/Tests/TestSocketIO/SocketAckManagerTest.swift
+++ b/Tests/TestSocketIO/SocketAckManagerTest.swift
@@ -21,7 +21,7 @@ class SocketAckManagerTest : XCTestCase {
         }
 
         ackManager.addAck(1, callback: callback)
-        ackManager.executeAck(1, with: itemsArray, onQueue: DispatchQueue.main)
+        ackManager.executeAck(1, with: itemsArray)
 
         waitForExpectations(timeout: 3.0, handler: nil)
     }
@@ -44,7 +44,7 @@ class SocketAckManagerTest : XCTestCase {
         }
 
         ackManager.addAck(1, callback: callback)
-        ackManager.timeoutAck(1, onQueue: DispatchQueue.main)
+        ackManager.timeoutAck(1)
 
         waitForExpectations(timeout: 0.2, handler: nil)
     }