diff --git a/src/AsyncHTTPRequest.cpp b/src/AsyncHTTPRequest.cpp
index 1591555..c62b3f9 100644
--- a/src/AsyncHTTPRequest.cpp
+++ b/src/AsyncHTTPRequest.cpp
@@ -61,7 +61,7 @@ private:
 AsyncHTTPRequest::AsyncHTTPRequest(): _readyState(ReadyState::Idle), _HTTPcode(0), _chunked(false), _debug(DEBUG_IOTA_HTTP_SET)
   , _timeout(DEFAULT_RX_TIMEOUT), _lastActivity(0), _requestStartTime(0), _requestEndTime(0), _URL(nullptr)
   , _connectedHost(nullptr), _connectedPort(-1), _client(nullptr), _contentLength(0), _contentRead(0)
-  , _readyStateChangeCB(nullptr), _readyStateChangeCBarg(nullptr), _onDataCB(nullptr), _onDataCBarg(nullptr)
+  , _readyStateChangeCB(nullptr), _readyStateChangeCBarg{}, _onDataCB(nullptr), _onDataCBarg(nullptr)
   , _request(nullptr), _response(nullptr), _chunks(nullptr), _headers(nullptr)
 {
 #ifdef ESP32
@@ -161,14 +161,14 @@ bool  AsyncHTTPRequest::open(const char* method, const char* URL)
   return _connect();
 }
 //**************************************************************************************************************
-void AsyncHTTPRequest::onReadyStateChange(readyStateChangeCB cb, void* arg)
+void AsyncHTTPRequest::onReadyStateChange(readyStateChangeCB cb, callback_arg_t arg)
 {
   _readyStateChangeCB = cb;
   _readyStateChangeCBarg = arg;
 }
 
 //**************************************************************************************************************
-void AsyncHTTPRequest::onReadyStateChangeArg(void* arg)
+void AsyncHTTPRequest::onReadyStateChangeArg(callback_arg_t arg)
 {
   _readyStateChangeCBarg = arg;
 }
diff --git a/src/AsyncHTTPRequest.h b/src/AsyncHTTPRequest.h
index 58a1f06..ff527f5 100644
--- a/src/AsyncHTTPRequest.h
+++ b/src/AsyncHTTPRequest.h
@@ -91,6 +91,8 @@ enum class ReadyState
     
 class AsyncHTTPRequest
 {
+    using callback_arg_t = void*;
+
     struct header
     {
       header*   next;
@@ -135,7 +137,7 @@ class AsyncHTTPRequest
       }
     };
 
-    using readyStateChangeCB = std::function<void(void*, AsyncHTTPRequest*, ReadyState readyState)>;
+    using readyStateChangeCB = std::function<void(callback_arg_t, AsyncHTTPRequest*, ReadyState readyState)>;
     using onDataCB = std::function<void(void*, AsyncHTTPRequest*, size_t available)>;
 
   public:
@@ -149,8 +151,8 @@ class AsyncHTTPRequest
     bool        debug() const;                                          // is debug on or off?
 
     bool        open(const char* method, const char* URL);              // Initiate a request
-    void        onReadyStateChange(readyStateChangeCB, void* arg = 0);  // Optional event handler for ready state change
-    void        onReadyStateChangeArg(void* arg = 0);                   // set event handlers arg
+    void        onReadyStateChange(readyStateChangeCB, callback_arg_t arg = 0);  // Optional event handler for ready state change
+    void        onReadyStateChangeArg(callback_arg_t arg = 0);                   // set event handlers arg
     // or you can simply poll readyState()
     void        setTimeout(int seconds);                                // overide default timeout (seconds)
 
@@ -217,7 +219,7 @@ class AsyncHTTPRequest
     size_t          _contentLength;             // content-length header value or sum of chunk headers
     size_t          _contentRead;               // number of bytes retrieved by user since last open()
     readyStateChangeCB  _readyStateChangeCB;    // optional callback for readyState change
-    void*           _readyStateChangeCBarg;     // associated user argument
+    callback_arg_t  _readyStateChangeCBarg;     // associated user argument
     onDataCB        _onDataCB;                  // optional callback when data received
     void*           _onDataCBarg;               // associated user argument