diff --git a/hardware/arduino/cores/arduino/Print.cpp b/hardware/arduino/cores/arduino/Print.cpp
index 4ee556dd8..fd689423a 100755
--- a/hardware/arduino/cores/arduino/Print.cpp
+++ b/hardware/arduino/cores/arduino/Print.cpp
@@ -45,7 +45,7 @@ void Print::write(const uint8_t *buffer, size_t size)
 
 void Print::print(const String &s)
 {
-  for (int i = 0; i < s.length(); i++) {
+  for (unsigned int i = 0; i < s.length(); i++) {
     write(s[i]);
   }
 }
diff --git a/hardware/arduino/cores/arduino/WString.h b/hardware/arduino/cores/arduino/WString.h
index cadddb947..56faf9a48 100644
--- a/hardware/arduino/cores/arduino/WString.h
+++ b/hardware/arduino/cores/arduino/WString.h
@@ -67,7 +67,7 @@ class String
     int	lastIndexOf( char ch, unsigned int fromIndex ) const;
     int	lastIndexOf( const String &str ) const;
     int	lastIndexOf( const String &str, unsigned int fromIndex ) const;
-    const unsigned int length( ) const { return _length; }
+    unsigned int length( ) const { return _length; }
     void setCharAt(unsigned int index, const char ch);
     unsigned char startsWith( const String &prefix ) const;
     unsigned char startsWith( const String &prefix, unsigned int toffset ) const;
diff --git a/hardware/arduino/cores/arduino/pins_arduino.c b/hardware/arduino/cores/arduino/pins_arduino.c
index 0c816e94d..62e10ad15 100755
--- a/hardware/arduino/cores/arduino/pins_arduino.c
+++ b/hardware/arduino/cores/arduino/pins_arduino.c
@@ -81,50 +81,50 @@
 #if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
 const uint16_t PROGMEM port_to_mode_PGM[] = {
 	NOT_A_PORT,
-	&DDRA,
-	&DDRB,
-	&DDRC,
-	&DDRD,
-	&DDRE,
-	&DDRF,
-	&DDRG,
-	&DDRH,
+	(uint16_t) &DDRA,
+	(uint16_t) &DDRB,
+	(uint16_t) &DDRC,
+	(uint16_t) &DDRD,
+	(uint16_t) &DDRE,
+	(uint16_t) &DDRF,
+	(uint16_t) &DDRG,
+	(uint16_t) &DDRH,
 	NOT_A_PORT,
-	&DDRJ,
-	&DDRK,
-	&DDRL,
+	(uint16_t) &DDRJ,
+	(uint16_t) &DDRK,
+	(uint16_t) &DDRL,
 };
 
 const uint16_t PROGMEM port_to_output_PGM[] = {
 	NOT_A_PORT,
-	&PORTA,
-	&PORTB,
-	&PORTC,
-	&PORTD,
-	&PORTE,
-	&PORTF,
-	&PORTG,
-	&PORTH,
+	(uint16_t) &PORTA,
+	(uint16_t) &PORTB,
+	(uint16_t) &PORTC,
+	(uint16_t) &PORTD,
+	(uint16_t) &PORTE,
+	(uint16_t) &PORTF,
+	(uint16_t) &PORTG,
+	(uint16_t) &PORTH,
 	NOT_A_PORT,
-	&PORTJ,
-	&PORTK,
-	&PORTL,
+	(uint16_t) &PORTJ,
+	(uint16_t) &PORTK,
+	(uint16_t) &PORTL,
 };
 
 const uint16_t PROGMEM port_to_input_PGM[] = {
 	NOT_A_PIN,
-	&PINA,
-	&PINB,
-	&PINC,
-	&PIND,
-	&PINE,
-	&PINF,
-	&PING,
-	&PINH,
+	(uint16_t) &PINA,
+	(uint16_t) &PINB,
+	(uint16_t) &PINC,
+	(uint16_t) &PIND,
+	(uint16_t) &PINE,
+	(uint16_t) &PINF,
+	(uint16_t) &PING,
+	(uint16_t) &PINH,
 	NOT_A_PIN,
-	&PINJ,
-	&PINK,
-	&PINL,
+	(uint16_t) &PINJ,
+	(uint16_t) &PINK,
+	(uint16_t) &PINL,
 };
 
 const uint8_t PROGMEM digital_pin_to_port_PGM[] = {
@@ -358,25 +358,25 @@ const uint8_t PROGMEM digital_pin_to_timer_PGM[] = {
 const uint16_t PROGMEM port_to_mode_PGM[] = {
 	NOT_A_PORT,
 	NOT_A_PORT,
-	&DDRB,
-	&DDRC,
-	&DDRD,
+	(uint16_t) &DDRB,
+	(uint16_t) &DDRC,
+	(uint16_t) &DDRD,
 };
 
 const uint16_t PROGMEM port_to_output_PGM[] = {
 	NOT_A_PORT,
 	NOT_A_PORT,
-	&PORTB,
-	&PORTC,
-	&PORTD,
+	(uint16_t) &PORTB,
+	(uint16_t) &PORTC,
+	(uint16_t) &PORTD,
 };
 
 const uint16_t PROGMEM port_to_input_PGM[] = {
 	NOT_A_PORT,
 	NOT_A_PORT,
-	&PINB,
-	&PINC,
-	&PIND,
+	(uint16_t) &PINB,
+	(uint16_t) &PINC,
+	(uint16_t) &PIND,
 };
 
 const uint8_t PROGMEM digital_pin_to_port_PGM[] = {
diff --git a/libraries/Ethernet/utility/socket.cpp b/libraries/Ethernet/utility/socket.cpp
index cad54a5e3..f9f4bb190 100644
--- a/libraries/Ethernet/utility/socket.cpp
+++ b/libraries/Ethernet/utility/socket.cpp
@@ -9,7 +9,6 @@ static uint16_t local_port;
  */
 uint8_t socket(SOCKET s, uint8_t protocol, uint16_t port, uint8_t flag)
 {
-  uint8_t ret;
   if ((protocol == SnMR::TCP) || (protocol == SnMR::UDP) || (protocol == SnMR::IPRAW) || (protocol == SnMR::MACRAW) || (protocol == SnMR::PPPOE))
   {
     close(s);
diff --git a/libraries/Ethernet/utility/w5100.cpp b/libraries/Ethernet/utility/w5100.cpp
index aaf3071f7..03aca0846 100644
--- a/libraries/Ethernet/utility/w5100.cpp
+++ b/libraries/Ethernet/utility/w5100.cpp
@@ -134,7 +134,7 @@ uint8_t W5100Class::write(uint16_t _addr, uint8_t _data)
 
 uint16_t W5100Class::write(uint16_t _addr, uint8_t *_buf, uint16_t _len)
 {
-  for (int i=0; i<_len; i++)
+  for (uint16_t i=0; i<_len; i++)
   {
     setSS();    
     SPI.transfer(0xF0);
@@ -160,7 +160,7 @@ uint8_t W5100Class::read(uint16_t _addr)
 
 uint16_t W5100Class::read(uint16_t _addr, uint8_t *_buf, uint16_t _len)
 {
-  for (int i=0; i<_len; i++)
+  for (uint16_t i=0; i<_len; i++)
   {
     setSS();
     SPI.transfer(0x0F);
diff --git a/libraries/SD/File.cpp b/libraries/SD/File.cpp
index ded622c85..b93466ec1 100644
--- a/libraries/SD/File.cpp
+++ b/libraries/SD/File.cpp
@@ -27,7 +27,7 @@ void File::write(const uint8_t *buf, size_t size) {
 }
 
 int File::peek() {
-  char c = SD.file.read();
+  int c = SD.file.read();
   if (c != -1) SD.file.seekCur(-1);
   return c;
 }