diff --git a/SocketIOClientSwift/SocketIOClient.swift b/SocketIOClientSwift/SocketIOClient.swift
index 3559c92..e38071c 100644
--- a/SocketIOClientSwift/SocketIOClient.swift
+++ b/SocketIOClientSwift/SocketIOClient.swift
@@ -432,7 +432,7 @@ public final class SocketIOClient: NSObject, SocketEngineClient {
         
         var handler: SocketEventHandler;
 
-        handler = SocketEventHandler(event: event) { data, ack in
+        handler = SocketEventHandler(event: event) { (data, ack: AckEmitter?) in
             self.handlers = ContiguousArray(self.handlers.filter { $0 != handler })
             callback?(data, ack)
         }
@@ -448,7 +448,7 @@ public final class SocketIOClient: NSObject, SocketEngineClient {
         
         var handler: SocketEventHandler;
 
-        handler = SocketEventHandler(event: event) { data, ack in
+        handler = SocketEventHandler(event: event) { (data, ack: AckEmitterObjectiveC?) in
             self.handlers = ContiguousArray(self.handlers.filter { $0 != handler })
             callback?(data, ack)
         }