diff --git a/PubSubClient/PubSubClient.cpp b/PubSubClient/PubSubClient.cpp
index cb9ca68..e5bf7cc 100755
--- a/PubSubClient/PubSubClient.cpp
+++ b/PubSubClient/PubSubClient.cpp
@@ -59,42 +59,42 @@ PubSubClient::PubSubClient(uint8_t *ip, uint16_t port, MQTT_CALLBACK_SIGNATURE,
    setStream(stream);
 }
 
-PubSubClient::PubSubClient(char* domain, uint16_t port, Client& client) {
+PubSubClient::PubSubClient(const char* domain, uint16_t port, Client& client) {
    setServer(domain,port);
    setClient(client);
    this->stream = NULL;
 }
-PubSubClient::PubSubClient(char* domain, uint16_t port, Client& client, Stream& stream) {
+PubSubClient::PubSubClient(const char* domain, uint16_t port, Client& client, Stream& stream) {
    setServer(domain,port);
    setClient(client);
    setStream(stream);
 }
-PubSubClient::PubSubClient(char* domain, uint16_t port, MQTT_CALLBACK_SIGNATURE, Client& client) {
+PubSubClient::PubSubClient(const char* domain, uint16_t port, MQTT_CALLBACK_SIGNATURE, Client& client) {
    setServer(domain,port);
    setCallback(callback);
    setClient(client);
    this->stream = NULL;
 }
-PubSubClient::PubSubClient(char* domain, uint16_t port, MQTT_CALLBACK_SIGNATURE, Client& client, Stream& stream) {
+PubSubClient::PubSubClient(const char* domain, uint16_t port, MQTT_CALLBACK_SIGNATURE, Client& client, Stream& stream) {
    setServer(domain,port);
    setCallback(callback);
    setClient(client);
    setStream(stream);
 }
 
-boolean PubSubClient::connect(char *id) {
+boolean PubSubClient::connect(const char *id) {
    return connect(id,NULL,NULL,0,0,0,0);
 }
 
-boolean PubSubClient::connect(char *id, char *user, char *pass) {
+boolean PubSubClient::connect(const char *id, const char *user, const char *pass) {
    return connect(id,user,pass,0,0,0,0);
 }
 
-boolean PubSubClient::connect(char *id, char* willTopic, uint8_t willQos, uint8_t willRetain, char* willMessage) {
+boolean PubSubClient::connect(const char *id, const char* willTopic, uint8_t willQos, boolean willRetain, const char* willMessage) {
    return connect(id,NULL,NULL,willTopic,willQos,willRetain,willMessage);
 }
 
-boolean PubSubClient::connect(char *id, char *user, char *pass, char* willTopic, uint8_t willQos, uint8_t willRetain, char* willMessage) {
+boolean PubSubClient::connect(const char *id, const char *user, const char *pass, const char* willTopic, uint8_t willQos, boolean willRetain, const char* willMessage) {
    if (!connected()) {
       int result = 0;
 
@@ -296,15 +296,15 @@ boolean PubSubClient::loop() {
    return false;
 }
 
-boolean PubSubClient::publish(char* topic, char* payload) {
-   return publish(topic,(uint8_t*)payload,strlen(payload),false);
+boolean PubSubClient::publish(const char* topic, const char* payload) {
+   return publish(topic,(const uint8_t*)payload,strlen(payload),false);
 }
 
-boolean PubSubClient::publish(char* topic, uint8_t* payload, unsigned int plength) {
+boolean PubSubClient::publish(const char* topic, const uint8_t* payload, unsigned int plength) {
    return publish(topic, payload, plength, false);
 }
 
-boolean PubSubClient::publish(char* topic, uint8_t* payload, unsigned int plength, boolean retained) {
+boolean PubSubClient::publish(const char* topic, const uint8_t* payload, unsigned int plength, boolean retained) {
    if (connected()) {
       // Leave room in the buffer for header and variable length field
       uint16_t length = 5;
@@ -321,8 +321,8 @@ boolean PubSubClient::publish(char* topic, uint8_t* payload, unsigned int plengt
    }
    return false;
 }
-#ifdef PROGMEM
-boolean PubSubClient::publish_P(char* topic, uint8_t* PROGMEM payload, unsigned int plength, boolean retained) {
+
+boolean PubSubClient::publish_P(const char* topic, const uint8_t* payload, unsigned int plength, boolean retained) {
    uint8_t llen = 0;
    uint8_t digit;
    unsigned int rc = 0;
@@ -366,7 +366,6 @@ boolean PubSubClient::publish_P(char* topic, uint8_t* PROGMEM payload, unsigned
 
    return rc == tlen + 4 + plength;
 }
-#endif
 
 boolean PubSubClient::write(uint8_t header, uint8_t* buf, uint16_t length) {
    uint8_t lenBuf[4];
@@ -395,11 +394,11 @@ boolean PubSubClient::write(uint8_t header, uint8_t* buf, uint16_t length) {
    return (rc == 1+llen+length);
 }
 
-boolean PubSubClient::subscribe(char* topic) {
+boolean PubSubClient::subscribe(const char* topic) {
   return subscribe(topic, 0);
 }
 
-boolean PubSubClient::subscribe(char* topic, uint8_t qos) {
+boolean PubSubClient::subscribe(const char* topic, uint8_t qos) {
    if (qos < 0 || qos > 1)
      return false;
 
@@ -412,14 +411,14 @@ boolean PubSubClient::subscribe(char* topic, uint8_t qos) {
       }
       buffer[length++] = (nextMsgId >> 8);
       buffer[length++] = (nextMsgId & 0xFF);
-      length = writeString(topic, buffer,length);
+      length = writeString((char*)topic, buffer,length);
       buffer[length++] = qos;
       return write(MQTTSUBSCRIBE|MQTTQOS1,buffer,length-5);
    }
    return false;
 }
 
-boolean PubSubClient::unsubscribe(char* topic) {
+boolean PubSubClient::unsubscribe(const char* topic) {
    if (connected()) {
       uint16_t length = 5;
       nextMsgId++;
@@ -442,8 +441,8 @@ void PubSubClient::disconnect() {
    lastInActivity = lastOutActivity = millis();
 }
 
-uint16_t PubSubClient::writeString(char* string, uint8_t* buf, uint16_t pos) {
-   char* idp = string;
+uint16_t PubSubClient::writeString(const char* string, uint8_t* buf, uint16_t pos) {
+   const char* idp = string;
    uint16_t i = 0;
    pos += 2;
    while (*idp) {
@@ -475,9 +474,10 @@ void PubSubClient::setServer(uint8_t * ip, uint16_t port) {
 void PubSubClient::setServer(IPAddress ip, uint16_t port) {
     this->ip = ip;
     this->port = port;
+    this->domain = NULL;
 }
 
-void PubSubClient::setServer(char * domain, uint16_t port) {
+void PubSubClient::setServer(const char * domain, uint16_t port) {
     this->domain = domain;
     this->port = port;
 }
diff --git a/PubSubClient/PubSubClient.h b/PubSubClient/PubSubClient.h
index f472774..1f8a3ba 100755
--- a/PubSubClient/PubSubClient.h
+++ b/PubSubClient/PubSubClient.h
@@ -58,9 +58,9 @@ private:
    uint16_t readPacket(uint8_t*);
    uint8_t readByte();
    boolean write(uint8_t header, uint8_t* buf, uint16_t length);
-   uint16_t writeString(char* string, uint8_t* buf, uint16_t pos);
+   uint16_t writeString(const char* string, uint8_t* buf, uint16_t pos);
    IPAddress ip;
-   char* domain;
+   const char* domain;
    uint16_t port;
    Stream* stream;
 public:
@@ -73,32 +73,30 @@ public:
    PubSubClient(uint8_t *, uint16_t, Client& client, Stream&);
    PubSubClient(uint8_t *, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client);
    PubSubClient(uint8_t *, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client, Stream&);
-   PubSubClient(char*, uint16_t, Client& client);
-   PubSubClient(char*, uint16_t, Client& client, Stream&);
-   PubSubClient(char*, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client);
-   PubSubClient(char*, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client, Stream&);
+   PubSubClient(const char*, uint16_t, Client& client);
+   PubSubClient(const char*, uint16_t, Client& client, Stream&);
+   PubSubClient(const char*, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client);
+   PubSubClient(const char*, uint16_t, MQTT_CALLBACK_SIGNATURE,Client& client, Stream&);
 
    void setServer(IPAddress ip, uint16_t port);
    void setServer(uint8_t * ip, uint16_t port);
-   void setServer(char * domain, uint16_t port);
+   void setServer(const char * domain, uint16_t port);
    void setCallback(MQTT_CALLBACK_SIGNATURE);
    void setClient(Client& client);
    void setStream(Stream& stream);
 
-   boolean connect(char *);
-   boolean connect(char *, char *, char *);
-   boolean connect(char *, char *, uint8_t, uint8_t, char *);
-   boolean connect(char *, char *, char *, char *, uint8_t, uint8_t, char*);
+   boolean connect(const char* id);
+   boolean connect(const char* id, const char* user, const char* pass);
+   boolean connect(const char* id, const char* willTopic, uint8_t willQos, boolean willRetain, const char* willMessage);
+   boolean connect(const char* id, const char* user, const char* pass, const char* willTopic, uint8_t willQos, boolean willRetain, const char* willMessage);
    void disconnect();
-   boolean publish(char *, char *);
-   boolean publish(char *, uint8_t *, unsigned int);
-   boolean publish(char *, uint8_t *, unsigned int, boolean);
-#ifdef PROGMEM
-   boolean publish_P(char *, uint8_t PROGMEM *, unsigned int, boolean);
-#endif
-   boolean subscribe(char *);
-   boolean subscribe(char *, uint8_t qos);
-   boolean unsubscribe(char *);
+   boolean publish(const char* topic, const char* payload);
+   boolean publish(const char* topic, const uint8_t * payload, unsigned int plength);
+   boolean publish(const char* topic, const uint8_t * payload, unsigned int plength, boolean retained);
+   boolean publish_P(const char* topic, const uint8_t * payload, unsigned int plength, boolean retained);
+   boolean subscribe(const char* topic);
+   boolean subscribe(const char* topic, uint8_t qos);
+   boolean unsubscribe(const char* topic);
    boolean loop();
    boolean connected();
 };