diff --git a/Sming/Core/Network/MqttClient.cpp b/Sming/Core/Network/MqttClient.cpp
index 9325126e94..5aead192cb 100644
--- a/Sming/Core/Network/MqttClient.cpp
+++ b/Sming/Core/Network/MqttClient.cpp
@@ -16,10 +16,23 @@
 #include "Clock.h"
 
 // Content length set to this value to indicate data refers to a stream, not a buffer
-#define MQTT_PUBLISH_STREAM 0
+static constexpr unsigned MQTT_PUBLISH_STREAM = 0;
 
-mqtt_serialiser_t MqttClient::serialiser;
-mqtt_parser_callbacks_t MqttClient::callbacks;
+static constexpr uint8_t MQTT_CONNECT_PROTOCOL = 4; // version 3.1.1
+
+const mqtt_parser_callbacks_t MqttClient::callbacks PROGMEM = {
+	.on_message_begin = staticOnMessageBegin,
+	.on_data_begin = staticOnDataBegin,
+	.on_data_payload = staticOnDataPayload,
+	.on_data_end = staticOnDataEnd,
+	.on_message_end = staticOnMessageEnd,
+};
+
+#define GET_CLIENT()                                                                                                   \
+	auto client = static_cast<MqttClient*>(userData);                                                                  \
+	if(client == nullptr) {                                                                                            \
+		return -1;                                                                                                     \
+	}
 
 static mqtt_message_t* createMessage(mqtt_type_t messageType)
 {
@@ -57,23 +70,14 @@ static bool copyString(mqtt_buffer_t& destBuffer, const String& sourceString)
 
 MqttClient::MqttClient(bool withDefaultPayloadParser, bool autoDestruct) : TcpClient(autoDestruct)
 {
-	// TODO:...
-	//	if(!bitSet(flags, MQTT_CLIENT_CALLBACKS)) {
-	callbacks.on_message_begin = staticOnMessageBegin;
-	callbacks.on_data_begin = staticOnDataBegin;
-	callbacks.on_data_payload = staticOnDataPayload;
-	callbacks.on_data_end = staticOnDataEnd;
-	callbacks.on_message_end = staticOnMessageEnd;
-	//	}
-
-	mqtt_parser_init(&parser, &callbacks);
+	mqtt_parser_init(&parser, const_cast<mqtt_parser_callbacks_t*>(&callbacks));
 	mqtt_serialiser_init(&serialiser);
 	mqtt_message_init(&incomingMessage);
 	mqtt_message_init(&connectMessage);
 
 	parser.data = this;
 	connectMessage.common.type = MQTT_TYPE_CONNECT;
-	connectMessage.connect.protocol_version = 4; // version 3.1.1
+	connectMessage.connect.protocol_version = MQTT_CONNECT_PROTOCOL;
 
 	if(withDefaultPayloadParser) {
 		setPayloadParser(defaultPayloadParser);
@@ -116,10 +120,7 @@ int MqttClient::staticOnMessageBegin(void* userData, mqtt_message_t* message)
 
 int MqttClient::staticOnDataBegin(void* userData, mqtt_message_t* message)
 {
-	MqttClient* client = static_cast<MqttClient*>(userData);
-	if(client == nullptr) {
-		return -1;
-	}
+	GET_CLIENT();
 
 	if(client->payloadParser) {
 		client->payloadState.offset = 0;
@@ -131,10 +132,7 @@ int MqttClient::staticOnDataBegin(void* userData, mqtt_message_t* message)
 
 int MqttClient::staticOnDataPayload(void* userData, mqtt_message_t* message, const char* data, size_t length)
 {
-	MqttClient* client = static_cast<MqttClient*>(userData);
-	if(client == nullptr) {
-		return -1;
-	}
+	GET_CLIENT();
 
 	if(client->payloadParser) {
 		return client->payloadParser(client->payloadState, message, data, length);
@@ -145,10 +143,7 @@ int MqttClient::staticOnDataPayload(void* userData, mqtt_message_t* message, con
 
 int MqttClient::staticOnDataEnd(void* userData, mqtt_message_t* message)
 {
-	MqttClient* client = static_cast<MqttClient*>(userData);
-	if(client == nullptr) {
-		return -1;
-	}
+	GET_CLIENT();
 
 	if(client->payloadParser) {
 		return client->payloadParser(client->payloadState, message, nullptr, MQTT_PAYLOAD_PARSER_END);
@@ -159,27 +154,29 @@ int MqttClient::staticOnDataEnd(void* userData, mqtt_message_t* message)
 
 int MqttClient::staticOnMessageEnd(void* userData, mqtt_message_t* message)
 {
-	MqttClient* client = static_cast<MqttClient*>(userData);
-	if(client == nullptr) {
-		return -1;
-	}
+	GET_CLIENT();
+	return client->onMessageEnd(message);
+}
 
+int MqttClient::onMessageEnd(mqtt_message_t* message)
+{
 	if(message->common.type == MQTT_TYPE_CONNACK) {
 		if(message->connack.return_code) {
 			// failure
-			clearBits(client->flags, MQTT_CLIENT_CONNECTED);
-			client->setTimeOut(1); // schedule the connection for closing
+			clearBits(flags, MQTT_CLIENT_CONNECTED);
+			setTimeOut(1); // schedule the connection for closing
 
 			return message->connack.return_code;
 		}
 
 		// success
-		client->setTimeOut(USHRT_MAX);
-		setBits(client->flags, MQTT_CLIENT_CONNECTED);
+		setTimeOut(USHRT_MAX);
+		setBits(flags, MQTT_CLIENT_CONNECTED);
 	}
 
-	if(client->eventHandler.contains(message->common.type)) {
-		return client->eventHandler[message->common.type](*client, message);
+	auto& handler = reinterpret_cast<const HandlerMap&>(eventHandlers)[message->common.type];
+	if(handler) {
+		return handler(*this, message);
 	}
 
 	return 0;
diff --git a/Sming/Core/Network/MqttClient.h b/Sming/Core/Network/MqttClient.h
index f2c943a3d5..694f17ff69 100644
--- a/Sming/Core/Network/MqttClient.h
+++ b/Sming/Core/Network/MqttClient.h
@@ -100,7 +100,7 @@ class MqttClient : protected TcpClient
 
 	void setEventHandler(mqtt_type_t type, MqttDelegate handler)
 	{
-		eventHandler[type] = handler;
+		eventHandlers[type] = handler;
 	}
 
 	/**
@@ -123,7 +123,7 @@ class MqttClient : protected TcpClient
 	 */
 	void setConnectedHandler(MqttDelegate handler)
 	{
-		eventHandler[MQTT_TYPE_CONNACK] = handler;
+		eventHandlers[MQTT_TYPE_CONNACK] = handler;
 	}
 
 	/**
@@ -134,8 +134,8 @@ class MqttClient : protected TcpClient
 	 */
 	void setPublishedHandler(MqttDelegate handler)
 	{
-		eventHandler[MQTT_TYPE_PUBACK] = handler;
-		eventHandler[MQTT_TYPE_PUBREC] = handler;
+		eventHandlers[MQTT_TYPE_PUBACK] = handler;
+		eventHandlers[MQTT_TYPE_PUBREC] = handler;
 	}
 
 	/**
@@ -145,7 +145,7 @@ class MqttClient : protected TcpClient
 	 */
 	void setMessageHandler(MqttDelegate handler)
 	{
-		eventHandler[MQTT_TYPE_PUBLISH] = handler;
+		eventHandlers[MQTT_TYPE_PUBLISH] = handler;
 	}
 
 	/**
@@ -233,6 +233,7 @@ class MqttClient : protected TcpClient
 	static int staticOnDataPayload(void* user_data, mqtt_message_t* message, const char* data, size_t length);
 	static int staticOnDataEnd(void* user_data, mqtt_message_t* message);
 	static int staticOnMessageEnd(void* user_data, mqtt_message_t* message);
+	int onMessageEnd(mqtt_message_t* message);
 
 #ifndef MQTT_NO_COMPAT
 	/** @deprecated This method is only for compatibility with the previous release and will be removed soon. */
@@ -286,7 +287,8 @@ class MqttClient : protected TcpClient
 	Url url;
 
 	// callbacks
-	HashMap<mqtt_type_t, MqttDelegate> eventHandler;
+	using HandlerMap = HashMap<mqtt_type_t, MqttDelegate>;
+	HandlerMap eventHandlers;
 	MqttPayloadParser payloadParser = nullptr;
 
 	// states
@@ -306,8 +308,8 @@ class MqttClient : protected TcpClient
 	mqtt_message_t incomingMessage;
 
 	// parsers and serializers
-	static mqtt_serialiser_t serialiser;
-	static mqtt_parser_callbacks_t callbacks;
+	mqtt_serialiser_t serialiser;
+	static const mqtt_parser_callbacks_t callbacks;
 	mqtt_parser_t parser;
 
 	// client flags