diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index d91026a15..e165136c3 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -83,7 +83,7 @@ void HardwareSerial::_tx_udr_empty_irq(void)
   // If interrupts are enabled, there must be more data in the output
   // buffer. Send the next byte
   unsigned char c = _tx_buffer[_tx_buffer_tail];
-  _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
+  _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_TX_BUFFER_SIZE;
 
   *_udr = c;
 
@@ -152,7 +152,7 @@ void HardwareSerial::end()
 
 int HardwareSerial::available(void)
 {
-  return (unsigned int)(SERIAL_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail) % SERIAL_BUFFER_SIZE;
+  return (unsigned int)(SERIAL_RX_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail) % SERIAL_RX_BUFFER_SIZE;
 }
 
 int HardwareSerial::peek(void)
@@ -171,7 +171,7 @@ int HardwareSerial::read(void)
     return -1;
   } else {
     unsigned char c = _rx_buffer[_rx_buffer_tail];
-    _rx_buffer_tail = (uint8_t)(_rx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
+    _rx_buffer_tail = (rx_buffer_index_t)(_rx_buffer_tail + 1) % SERIAL_RX_BUFFER_SIZE;
     return c;
   }
 }
@@ -207,7 +207,7 @@ size_t HardwareSerial::write(uint8_t c)
     sbi(*_ucsra, TXC0);
     return 1;
   }
-  uint8_t i = (_tx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
+  tx_buffer_index_t i = (_tx_buffer_head + 1) % SERIAL_TX_BUFFER_SIZE;
 	
   // If the output buffer is full, there's nothing for it other than to 
   // wait for the interrupt handler to empty it a bit
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.h b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
index 226bf57a7..b96e5d058 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
@@ -32,10 +32,24 @@
 // using a ring buffer (I think), in which head is the index of the location
 // to which to write the next incoming character and tail is the index of the
 // location from which to read.
+#if !(defined(SERIAL_TX_BUFFER_SIZE) && defined(SERIAL_RX_BUFFER_SIZE))
 #if (RAMEND < 1000)
-  #define SERIAL_BUFFER_SIZE 16
+#define SERIAL_TX_BUFFER_SIZE 16
+#define SERIAL_RX_BUFFER_SIZE 16
 #else
-  #define SERIAL_BUFFER_SIZE 64
+#define SERIAL_TX_BUFFER_SIZE 64
+#define SERIAL_RX_BUFFER_SIZE 64
+#endif
+#endif
+#if (SERIAL_TX_BUFFER_SIZE>256)
+typedef uint16_t tx_buffer_index_t;
+#else
+typedef uint8_t tx_buffer_index_t;
+#endif
+#if  (SERIAL_RX_BUFFER_SIZE>256)
+typedef uint16_t rx_buffer_index_t;
+#else
+typedef uint8_t rx_buffer_index_t;
 #endif
 
 // Define config for Serial.begin(baud, config);
@@ -76,16 +90,16 @@ class HardwareSerial : public Stream
     // Has any byte been written to the UART since begin()
     bool _written;
 
-    volatile uint8_t _rx_buffer_head;
-    volatile uint8_t _rx_buffer_tail;
-    volatile uint8_t _tx_buffer_head;
-    volatile uint8_t _tx_buffer_tail;
+    volatile rx_buffer_index_t _rx_buffer_head;
+    volatile rx_buffer_index_t _rx_buffer_tail;
+    volatile tx_buffer_index_t _tx_buffer_head;
+    volatile tx_buffer_index_t _tx_buffer_tail;
 
     // Don't put any members after these buffers, since only the first
     // 32 bytes of this struct can be accessed quickly using the ldd
     // instruction.
-    unsigned char _rx_buffer[SERIAL_BUFFER_SIZE];
-    unsigned char _tx_buffer[SERIAL_BUFFER_SIZE];
+    unsigned char _rx_buffer[SERIAL_RX_BUFFER_SIZE];
+    unsigned char _tx_buffer[SERIAL_TX_BUFFER_SIZE];
 
   public:
     inline HardwareSerial(
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial_private.h b/hardware/arduino/avr/cores/arduino/HardwareSerial_private.h
index fa20e553b..ea41028b1 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial_private.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial_private.h
@@ -99,7 +99,7 @@ void HardwareSerial::_rx_complete_irq(void)
     // No Parity error, read byte and store it in the buffer if there is
     // room
     unsigned char c = *_udr;
-    uint8_t i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
+    rx_buffer_index_t i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_RX_BUFFER_SIZE;
 
     // if we should be storing the received character into the location
     // just before the tail (meaning that the head would advance to the