diff --git a/SocketIOClientSwift/SocketIOClient.swift b/SocketIOClientSwift/SocketIOClient.swift
index aa6fdf8..c4f2e64 100644
--- a/SocketIOClientSwift/SocketIOClient.swift
+++ b/SocketIOClientSwift/SocketIOClient.swift
@@ -430,8 +430,8 @@ public final class SocketIOClient: NSObject, SocketEngineClient {
     public func once(event: String, callback: NormalCallback) {
         Logger.log("Adding once handler for event: %@", type: logType, args: event)
         
-        let handler = SocketEventHandler(event: event) { data: NSArray?, ack: AckEmitter? in
-            handlers = ContiguousArray(handlers.filter { $0 != handler })
+        let handler = SocketEventHandler(event: event) { data, ack in
+            self.handlers = ContiguousArray(self.handlers.filter { $0 != handler })
             callback?(data, ack)
         }
 
@@ -444,8 +444,8 @@ public final class SocketIOClient: NSObject, SocketEngineClient {
     public func once(event event: String, callback: NormalCallbackObjectiveC) {
         Logger.log("Adding once handler for event: %@", type: logType, args: event)
         
-        let handler = SocketEventHandler(event: event) { data: NSArray?, ack: AckEmitterObjectiveC? in
-            handlers = ContiguousArray(handlers.filter { $0 != handler })
+        let handler = SocketEventHandler(event: event) { data, ack in
+            self.handlers = ContiguousArray(self.handlers.filter { $0 != handler })
             callback?(data, ack)
         }