diff --git a/cores/esp8266/Client.h b/cores/esp8266/Client.h
index cbdd6ae0b..6cb99a04b 100644
--- a/cores/esp8266/Client.h
+++ b/cores/esp8266/Client.h
@@ -26,7 +26,7 @@
 class Client: public Stream {
 
     public:
-        virtual int connect(CONST IPAddress& ip, uint16_t port) =0;
+        virtual int connect(IPAddress ip, uint16_t port) =0;
         virtual int connect(const char *host, uint16_t port) =0;
         virtual size_t write(uint8_t) =0;
         virtual size_t write(const uint8_t *buf, size_t size) =0;
@@ -34,15 +34,19 @@ class Client: public Stream {
         virtual int read() = 0;
         virtual int read(uint8_t *buf, size_t size) = 0;
         virtual int peek() = 0;
-        virtual bool flush(unsigned int maxWaitMs = 0) = 0;
-        virtual bool stop(unsigned int maxWaitMs = 0) = 0;
+        virtual void flush() = 0;
+        virtual void stop() = 0;
         virtual uint8_t connected() = 0;
         virtual operator bool() = 0;
     protected:
-        CONST uint8_t* rawIPAddress(CONST IPAddress& addr) {
+        uint8_t* rawIPAddress(IPAddress& addr) {
             return addr.raw_address();
         }
-        ;
+#if LWIP_VERSION_MAJOR != 1
+        const uint8_t* rawIPAddress(const IPAddress& addr) {
+            return addr.raw_address();
+        }
+#endif
 };
 
 #endif
diff --git a/cores/esp8266/Udp.h b/cores/esp8266/Udp.h
index ba2d5e371..de5127b18 100644
--- a/cores/esp8266/Udp.h
+++ b/cores/esp8266/Udp.h
@@ -79,13 +79,18 @@ class UDP: public Stream {
         virtual void flush() =0;	// Finish reading the current packet
 
         // Return the IP address of the host who sent the current incoming packet
-        virtual IPAddress remoteIP() const =0;
+        virtual IPAddress remoteIP() =0;
         // Return the port of the host who sent the current incoming packet
-        virtual uint16_t remotePort() const =0;
+        virtual uint16_t remotePort() =0;
     protected:
-        CONST uint8_t* rawIPAddress(CONST IPAddress& addr) {
+        uint8_t* rawIPAddress(IPAddress& addr) {
             return addr.raw_address();
         }
+#if LWIP_VERSION_MAJOR != 1
+        const uint8_t* rawIPAddress(const IPAddress& addr) {
+            return addr.raw_address();
+        }
+#endif
 };
 
 #endif
diff --git a/libraries/ESP8266WiFi/src/WiFiClient.cpp b/libraries/ESP8266WiFi/src/WiFiClient.cpp
index 4e100a032..2d7b5ac46 100644
--- a/libraries/ESP8266WiFi/src/WiFiClient.cpp
+++ b/libraries/ESP8266WiFi/src/WiFiClient.cpp
@@ -137,7 +137,7 @@ int WiFiClient::connect(const String& host, uint16_t port)
     return connect(host.c_str(), port);
 }
 
-int WiFiClient::connect(CONST IPAddress& ip, uint16_t port)
+int WiFiClient::connect(IPAddress ip, uint16_t port)
 {
     if (_client) {
         stop();
diff --git a/libraries/ESP8266WiFi/src/WiFiClient.h b/libraries/ESP8266WiFi/src/WiFiClient.h
index cd83fcbcb..31f6d105a 100644
--- a/libraries/ESP8266WiFi/src/WiFiClient.h
+++ b/libraries/ESP8266WiFi/src/WiFiClient.h
@@ -53,29 +53,31 @@ public:
   WiFiClient& operator=(const WiFiClient&);
 
   uint8_t status();
-  virtual int connect(CONST IPAddress& ip, uint16_t port);
-  virtual int connect(const char *host, uint16_t port);
+  virtual int connect(IPAddress ip, uint16_t port) override;
+  virtual int connect(const char *host, uint16_t port) override;
   virtual int connect(const String& host, uint16_t port);
-  virtual size_t write(uint8_t);
-  virtual size_t write(const uint8_t *buf, size_t size);
+  virtual size_t write(uint8_t) override;
+  virtual size_t write(const uint8_t *buf, size_t size) override;
   virtual size_t write_P(PGM_P buf, size_t size);
   size_t write(Stream& stream);
 
   // This one is deprecated, use write(Stream& instead)
   size_t write(Stream& stream, size_t unitSize) __attribute__ ((deprecated));
 
-  virtual int available();
-  virtual int read();
-  virtual int read(uint8_t *buf, size_t size);
-  virtual int peek();
+  virtual int available() override;
+  virtual int read() override;
+  virtual int read(uint8_t *buf, size_t size) override;
+  virtual int peek() override;
   virtual size_t peekBytes(uint8_t *buffer, size_t length);
   size_t peekBytes(char *buffer, size_t length) {
     return peekBytes((uint8_t *) buffer, length);
   }
-  virtual bool flush(unsigned int maxWaitMs = 0);
-  virtual bool stop(unsigned int maxWaitMs = 0);
-  virtual uint8_t connected();
-  virtual operator bool();
+  virtual void flush() override { (void)flush(0); }
+  virtual void stop() override { (void)stop(0); }
+  bool flush(unsigned int maxWaitMs);
+  bool stop(unsigned int maxWaitMs);
+  virtual uint8_t connected() override;
+  virtual operator bool() override;
 
   IPAddress remoteIP();
   uint16_t  remotePort();
diff --git a/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp b/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp
index 84be20b53..b47d7c21e 100644
--- a/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp
+++ b/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp
@@ -95,7 +95,7 @@ WiFiClientSecure::WiFiClientSecure(ClientContext* client, bool usePMEM,
     _ssl->connectServer(client, _timeout);
 }
 
-int WiFiClientSecure::connect(CONST IPAddress& ip, uint16_t port)
+int WiFiClientSecure::connect(IPAddress ip, uint16_t port)
 {
     if (!WiFiClient::connect(ip, port)) {
         return 0;
diff --git a/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.h b/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.h
index b1ae65d57..9958c4620 100644
--- a/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.h
+++ b/libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.h
@@ -35,7 +35,7 @@ public:
   WiFiClientSecure() __attribute__((deprecated("Upgrade to BearSSL is advised, check https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266WiFi/src/WiFiClientSecure.h#L25-L99")));
   ~WiFiClientSecure() override;
 
-  int connect(CONST IPAddress& ip, uint16_t port) override;
+  int connect(IPAddress ip, uint16_t port) override;
   int connect(const String& host, uint16_t port) override;
   int connect(const char* name, uint16_t port) override;
 
@@ -51,7 +51,8 @@ public:
   int read() override;
   int peek() override;
   size_t peekBytes(uint8_t *buffer, size_t length) override;
-  bool stop(unsigned int maxWaitMs = 0) override;
+  void stop() override { (void)stop(0); }
+  bool stop(unsigned int maxWaitMs);
 
   bool setCACert(const uint8_t* pk, size_t size);
   bool setCertificate(const uint8_t* pk, size_t size);
diff --git a/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp b/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp
index 67f0df6e6..8d1eee72e 100644
--- a/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp
+++ b/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp
@@ -210,7 +210,7 @@ bool WiFiClientSecure::flush(unsigned int maxWaitMs) {
   return WiFiClient::flush(maxWaitMs);
 }
 
-int WiFiClientSecure::connect(CONST IPAddress& ip, uint16_t port) {
+int WiFiClientSecure::connect(IPAddress ip, uint16_t port) {
   if (!WiFiClient::connect(ip, port)) {
     return 0;
   }
diff --git a/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h b/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h
index c9d4f4fb3..54d47616e 100644
--- a/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h
+++ b/libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.h
@@ -37,7 +37,7 @@ class WiFiClientSecure : public WiFiClient {
     WiFiClientSecure(const WiFiClientSecure &rhs);
     ~WiFiClientSecure() override;
 
-    int connect(CONST IPAddress& ip, uint16_t port) override;
+    int connect(IPAddress ip, uint16_t port) override;
     int connect(const String& host, uint16_t port) override;
     int connect(const char* name, uint16_t port) override;
 
@@ -56,8 +56,10 @@ class WiFiClientSecure : public WiFiClient {
     int read() override;
     int peek() override;
     size_t peekBytes(uint8_t *buffer, size_t length) override;
-    bool flush(unsigned int maxWaitMs = 0) override;
-    bool stop(unsigned int maxWaitMs = 0) override;
+    bool flush(unsigned int maxWaitMs);
+    bool stop(unsigned int maxWaitMs);
+    void flush() override { (void)flush(0); }
+    void stop() override { (void)stop(0); }
 
     // Allow sessions to be saved/restored automatically to a memory area
     void setSession(Session *session) { _session = session; }
diff --git a/libraries/ESP8266WiFi/src/WiFiUdp.cpp b/libraries/ESP8266WiFi/src/WiFiUdp.cpp
index 8de4cc4ff..a0a5c1d4e 100644
--- a/libraries/ESP8266WiFi/src/WiFiUdp.cpp
+++ b/libraries/ESP8266WiFi/src/WiFiUdp.cpp
@@ -231,7 +231,7 @@ void WiFiUDP::flush()
     endPacket();
 }
 
-IPAddress WiFiUDP::remoteIP() const
+IPAddress WiFiUDP::remoteIP()
 {
     if (!_ctx)
         return INADDR_ANY;
@@ -239,7 +239,7 @@ IPAddress WiFiUDP::remoteIP() const
     return _ctx->getRemoteAddress();
 }
 
-uint16_t WiFiUDP::remotePort() const
+uint16_t WiFiUDP::remotePort()
 {
     if (!_ctx)
         return 0;
diff --git a/libraries/ESP8266WiFi/src/WiFiUdp.h b/libraries/ESP8266WiFi/src/WiFiUdp.h
index fb205513c..a1cf42be1 100644
--- a/libraries/ESP8266WiFi/src/WiFiUdp.h
+++ b/libraries/ESP8266WiFi/src/WiFiUdp.h
@@ -95,9 +95,9 @@ public:
   void flush() override;	// Finish reading the current packet
 
   // Return the IP address of the host who sent the current incoming packet
-  IPAddress remoteIP() const override;
+  IPAddress remoteIP() override;
   // Return the port of the host who sent the current incoming packet
-  uint16_t remotePort() const override;
+  uint16_t remotePort() override;
   // Return the destination address for incoming packets,
   // useful to distinguish multicast and ordinary packets
   IPAddress destinationIP() const;
diff --git a/libraries/Ethernet/src/EthernetClient.cpp b/libraries/Ethernet/src/EthernetClient.cpp
index b03e2c495..942c4fca8 100644
--- a/libraries/Ethernet/src/EthernetClient.cpp
+++ b/libraries/Ethernet/src/EthernetClient.cpp
@@ -35,7 +35,7 @@ int EthernetClient::connect(const char* host, uint16_t port) {
   }
 }
 
-int EthernetClient::connect(CONST IPAddress& ip, uint16_t port) {
+int EthernetClient::connect(IPAddress ip, uint16_t port) {
   if (_sock != MAX_SOCK_NUM)
     return 0;
 
@@ -119,15 +119,13 @@ int EthernetClient::peek() {
   return b;
 }
 
-bool EthernetClient::flush(unsigned int maxWaitMs) {
-  (void)maxWaitMs;
+void EthernetClient::flush() {
   ::flush(_sock);
-  return true;
 }
 
-bool EthernetClient::stop(unsigned int maxWaitMs) {
+void EthernetClient::stop() {
   if (_sock == MAX_SOCK_NUM)
-    return true;
+    return;
 
   // attempt to close the connection gracefully (send a FIN to other side)
   disconnect(_sock);
@@ -135,27 +133,20 @@ bool EthernetClient::stop(unsigned int maxWaitMs) {
 
   // wait up to a second for the connection to close
   uint8_t s;
-  if (maxWaitMs == 0)
-    maxWaitMs = 1000;
   do {
     s = status();
     if (s == SnSR::CLOSED)
       break; // exit the loop
     delay(1);
-  } while (millis() - start < maxWaitMs);
-
-  bool ret = true;
+  } while (millis() - start < 1000);
 
   // if it hasn't closed, close it forcefully
   if (s != SnSR::CLOSED) {
-    ret = false;
     close(_sock);
   }
 
   EthernetClass::_server_port[_sock] = 0;
   _sock = MAX_SOCK_NUM;
-
-  return ret;
 }
 
 uint8_t EthernetClient::connected() {
diff --git a/libraries/Ethernet/src/EthernetClient.h b/libraries/Ethernet/src/EthernetClient.h
index 0ea3f6ca0..16e2500bc 100644
--- a/libraries/Ethernet/src/EthernetClient.h
+++ b/libraries/Ethernet/src/EthernetClient.h
@@ -12,7 +12,7 @@ public:
   EthernetClient(uint8_t sock);
 
   uint8_t status();
-  virtual int connect(CONST IPAddress& ip, uint16_t port);
+  virtual int connect(IPAddress ip, uint16_t port);
   virtual int connect(const char *host, uint16_t port);
   virtual size_t write(uint8_t);
   virtual size_t write(const uint8_t *buf, size_t size);
@@ -20,8 +20,8 @@ public:
   virtual int read();
   virtual int read(uint8_t *buf, size_t size);
   virtual int peek();
-  virtual bool flush(unsigned int maxWaitMs = 0);
-  virtual bool stop(unsigned int maxWaitMs = 0);
+  virtual void flush();
+  virtual void stop();
   virtual uint8_t connected();
   virtual operator bool();
   virtual bool operator==(const bool value) { return bool() == value; }
diff --git a/libraries/Ethernet/src/EthernetUdp.h b/libraries/Ethernet/src/EthernetUdp.h
index d4feb41af..1e928d88a 100644
--- a/libraries/Ethernet/src/EthernetUdp.h
+++ b/libraries/Ethernet/src/EthernetUdp.h
@@ -94,9 +94,9 @@ public:
   virtual void flush();	// Finish reading the current packet
 
   // Return the IP address of the host who sent the current incoming packet
-  virtual IPAddress remoteIP() const { return _remoteIP; };
+  virtual IPAddress remoteIP() { return _remoteIP; };
   // Return the port of the host who sent the current incoming packet
-  virtual uint16_t remotePort() const { return _remotePort; };
+  virtual uint16_t remotePort() { return _remotePort; };
 };
 
 #endif
diff --git a/libraries/Wire/Wire.cpp b/libraries/Wire/Wire.cpp
index e3ce0d7b6..88103650d 100644
--- a/libraries/Wire/Wire.cpp
+++ b/libraries/Wire/Wire.cpp
@@ -265,6 +265,13 @@ void TwoWire::onRequestService(void)
 	user_onRequest();
 }
 
+void TwoWire::onReceive( void (*function)(int) ) {
+  // arduino api compatibility fixer:
+  // really hope size parameter will not exceed 2^31 :)
+  static_assert(sizeof(int) == sizeof(size_t), "something is wrong in Arduino kingdom");
+  user_onReceive = reinterpret_cast<void(*)(size_t)>(function);
+}
+
 void TwoWire::onReceive( void (*function)(size_t) ) {
   user_onReceive = function;
 }
diff --git a/libraries/Wire/Wire.h b/libraries/Wire/Wire.h
index 79d47ec14..8f2a37394 100644
--- a/libraries/Wire/Wire.h
+++ b/libraries/Wire/Wire.h
@@ -76,7 +76,8 @@ class TwoWire : public Stream
     virtual int read(void);
     virtual int peek(void);
     virtual void flush(void);
-    void onReceive( void (*)(size_t) );
+    void onReceive( void (*)(int) );    // arduino api
+    void onReceive( void (*)(size_t) ); // legacy esp8266 backward compatibility
     void onRequest( void (*)(void) );
 
     inline size_t write(unsigned long n) { return write((uint8_t)n); }