diff --git a/SocketIO-MacTests/SocketObjectiveCTest.m b/SocketIO-MacTests/SocketObjectiveCTest.m
index 6043a24..2270a42 100644
--- a/SocketIO-MacTests/SocketObjectiveCTest.m
+++ b/SocketIO-MacTests/SocketObjectiveCTest.m
@@ -21,7 +21,8 @@
 - (void)setUp {
     [super setUp];
     NSURL* url = [[NSURL alloc] initWithString:@"http://localhost"];
-    self.socket = [[SocketIOClient alloc] initWithSocketURL:url options:nil];
+    self.socket = [[SocketIOClient alloc] initWithSocketURL:url
+                                                    options:@{@"handleQueue": dispatch_queue_create(nil, DISPATCH_QUEUE_SERIAL)}];
 }
 
 - (void)testOnSyntax {
diff --git a/SocketIO-MacTests/SocketSideEffectTest.swift b/SocketIO-MacTests/SocketSideEffectTest.swift
index 7f4bba6..2e377c5 100644
--- a/SocketIO-MacTests/SocketSideEffectTest.swift
+++ b/SocketIO-MacTests/SocketSideEffectTest.swift
@@ -16,7 +16,8 @@ class SocketSideEffectTest: XCTestCase {
     
     override func setUp() {
         super.setUp()
-        socket = SocketIOClient(socketURL: URL(string: "http://localhost/")!)
+        socket = SocketIOClient(socketURL: URL(string: "http://localhost/")!,
+                                options: [.handleQueue(DispatchQueue(label: "handleQueue", attributes: .serial, target: nil))])
         socket.setTestable()
     }
     
diff --git a/Source/SocketAckManager.swift b/Source/SocketAckManager.swift
index b7c050a..cda532f 100644
--- a/Source/SocketAckManager.swift
+++ b/Source/SocketAckManager.swift
@@ -56,19 +56,17 @@ struct SocketAckManager {
         acks.insert(SocketAck(ack: ack, callback: callback))
     }
     
+    /// Should be called on handle queue
     mutating func executeAck(_ ack: Int, items: [AnyObject]) {
         let callback = acks.remove(SocketAck(ack: ack))
-
-        DispatchQueue.main.async {
-            callback?.callback(items)
-        }
+        
+        callback?.callback(items)
     }
     
+    /// Should be called on handle queue
     mutating func timeoutAck(_ ack: Int) {
         let callback = acks.remove(SocketAck(ack: ack))
         
-        DispatchQueue.main.async {
-            callback?.callback(["NO ACK"])
-        }
+        callback?.callback(["NO ACK"])
     }
 }
diff --git a/Source/SocketIOClient.swift b/Source/SocketIOClient.swift
index 793af06..4beda6b 100644
--- a/Source/SocketIOClient.swift
+++ b/Source/SocketIOClient.swift
@@ -60,6 +60,7 @@ public final class SocketIOClient : NSObject, SocketEngineClient, SocketParsable
     private var reconnecting = false
 
     private(set) var currentAck = -1
+    // Handle queue also controls access to ackManager
     private(set) var handleQueue = DispatchQueue.main
     private(set) var reconnectAttempts = -1
 
@@ -162,7 +163,10 @@ public final class SocketIOClient : NSObject, SocketEngineClient, SocketParsable
 
         return {[weak self, ack = currentAck] timeout, callback in
             if let this = self {
-                this.ackHandlers.addAck(ack, callback: callback)
+                this.handleQueue.sync() {
+                    this.ackHandlers.addAck(ack, callback: callback)
+                }
+                
                 this._emit(items, ack: ack)
 
                 if timeout != 0 {
@@ -294,7 +298,9 @@ public final class SocketIOClient : NSObject, SocketEngineClient, SocketParsable
 
         DefaultSocketLogger.Logger.log("Handling ack: %@ with data: %@", type: logType, args: ack, data)
 
-        ackHandlers.executeAck(ack, items: data)
+        handleQueue.async() {
+            self.ackHandlers.executeAck(ack, items: data)
+        }
     }
 
     /// Causes an event to be handled. Only use if you know what you're doing.