diff --git a/build/shared/lib/keywords.txt b/build/shared/lib/keywords.txt
index 730de4e75..e69248cfb 100644
--- a/build/shared/lib/keywords.txt
+++ b/build/shared/lib/keywords.txt
@@ -164,6 +164,7 @@ Serial	KEYWORD3	Serial
 Serial1	KEYWORD3	Serial
 Serial2	KEYWORD3	Serial
 Serial3	KEYWORD3	Serial
+Serial4	KEYWORD3	Serial
 begin	KEYWORD2	Serial_Begin
 end	KEYWORD2	Serial_End
 peek	KEYWORD2	Serial_Peek
diff --git a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a
index db4a697f6..a4074053f 100644
Binary files a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a and b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a differ
diff --git a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a.txt b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a.txt
index b102bde18..480bd2f87 100644
--- a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a.txt
+++ b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a.txt
@@ -24,7 +24,7 @@ pmc.o:
 00000000 T PMC_IsPeripheralEnabled
 
 pwmc.o:
-00000000 r C.9.6844
+00000000 r C.9.6937
 00000000 t FindClockConfiguration
 00000000 T PWMC_ConfigureChannel
 00000000 T PWMC_ConfigureChannelExt
@@ -52,14 +52,14 @@ pwmc.o:
 00000000 T PWMC_SetSyncChannelUpdateUnlock
 00000000 T PWMC_WriteBuffer
          U __assert_func
-00000000 r __func__.5653
-00000000 r __func__.5664
-00000000 r __func__.5679
-00000000 r __func__.5690
-00000000 r __func__.5701
-00000000 r __func__.5708
-00000000 r __func__.5792
-00000000 r __func__.5798
+00000000 r __func__.5717
+00000000 r __func__.5728
+00000000 r __func__.5743
+00000000 r __func__.5754
+00000000 r __func__.5765
+00000000 r __func__.5772
+00000000 r __func__.5856
+00000000 r __func__.5862
 
 rtc.o:
 00000000 T RTC_ClearSCCR
@@ -75,9 +75,9 @@ rtc.o:
 00000000 T RTC_SetTime
 00000000 T RTC_SetTimeAlarm
          U __assert_func
-00000000 r __func__.5650
-00000000 r __func__.5659
-00000000 r __func__.5664
+00000000 r __func__.5714
+00000000 r __func__.5723
+00000000 r __func__.5728
 
 rtt.o:
 00000000 T RTT_EnableIT
@@ -86,8 +86,8 @@ rtt.o:
 00000000 T RTT_SetAlarm
 00000000 T RTT_SetPrescaler
          U __assert_func
-00000000 r __func__.5657
-00000000 r __func__.5665
+00000000 r __func__.5721
+00000000 r __func__.5729
 
 spi.o:
          U PMC_EnablePeripheral
@@ -108,9 +108,9 @@ tc.o:
 00000000 T TC_Start
 00000000 T TC_Stop
          U __assert_func
-00000000 r __func__.5652
-00000000 r __func__.5658
-00000000 r __func__.5664
+00000000 r __func__.5716
+00000000 r __func__.5722
+00000000 r __func__.5728
 
 timetick.o:
 00000000 T GetTickCount
@@ -137,18 +137,18 @@ twi.o:
 00000000 T TWI_TransferComplete
 00000000 T TWI_WriteByte
          U __assert_func
-00000000 r __func__.6025
-00000000 r __func__.6040
-00000000 r __func__.6044
-00000000 r __func__.6051
-00000000 r __func__.6055
-00000000 r __func__.6060
-00000000 r __func__.6068
-00000000 r __func__.6082
-00000000 r __func__.6087
-00000000 r __func__.6091
-00000000 r __func__.6096
-00000000 r __func__.6100
+00000000 r __func__.6089
+00000000 r __func__.6104
+00000000 r __func__.6108
+00000000 r __func__.6115
+00000000 r __func__.6119
+00000000 r __func__.6124
+00000000 r __func__.6132
+00000000 r __func__.6146
+00000000 r __func__.6151
+00000000 r __func__.6155
+00000000 r __func__.6160
+00000000 r __func__.6164
 
 usart.o:
 00000000 T USART_Configure
@@ -167,7 +167,7 @@ usart.o:
 00000000 T USART_Write
 00000000 T USART_WriteBuffer
          U __assert_func
-00000000 r __func__.5946
+00000000 r __func__.6010
 
 wdt.o:
 00000000 T WDT_Disable
diff --git a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
index 817b9ed18..ae8634e8d 100644
--- a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
+++ b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
@@ -35,12 +35,12 @@
  *  11       TIOA8 |  PD7
  *  12       TIOB8 |  PD8
  *  13       TIOB0 |  PB27
- *  14   TX3 TXD2  |  PD4
- *  15   RX3 RXD2  |  PD5
+ *  14   TX3 TXD3  |  PD4
+ *  15   RX3 RXD3  |  PD5
  *  16   TX2 TXD1  |  PA13
  *  17   RX2 RXD1  |  PA12
- *  18   TX1       |  PA11
- *  19   RX1       |  PA10
+ *  18   TX1 TXD0  |  PA11
+ *  19   RX1 RXD0  |  PA10
  *  20   SDA       |  PB12 (this pin is level adapted to 5V)
  *  21   SCL       |  PB13 (this pin is level adapted to 5V)
  *  22             |  PB26
@@ -260,7 +260,7 @@ extern const PinDescription g_APinDescription[]=
   { PIOA, PIO_PA11A_TXD0|PIO_PA10A_RXD0, ID_PIOA, PIO_PERIPH_A, PIO_DEFAULT, (PIN_ATTR_DIGITAL|PIN_ATTR_COMBO), NO_ADC, NO_ADC, NO_PWM, NO_TC },
   // 83 - USART1 (Serial3) all pins
   { PIOA, PIO_PA13A_TXD1|PIO_PA12A_RXD1, ID_PIOA, PIO_PERIPH_A, PIO_DEFAULT, (PIN_ATTR_DIGITAL|PIN_ATTR_COMBO), NO_ADC, NO_ADC, NO_PWM, NO_TC },
-  // 84 - USART2 (Serial4) all pins
+  // 84 - USART3 (Serial4) all pins
   { PIOD, PIO_PD4B_TXD3|PIO_PD5B_RXD3, ID_PIOD, PIO_PERIPH_B, PIO_DEFAULT, (PIN_ATTR_DIGITAL|PIN_ATTR_COMBO), NO_ADC, NO_ADC, NO_PWM, NO_TC },
 
   // END
@@ -290,7 +290,7 @@ RingBuffer rx_buffer4 ;
 
 USARTClass Serial2( USART0, USART0_IRQn, ID_USART0, &rx_buffer2 ) ;
 USARTClass Serial3( USART1, USART1_IRQn, ID_USART1, &rx_buffer3 ) ;
-USARTClass Serial4( USART2, USART2_IRQn, ID_USART2, &rx_buffer4 ) ;
+USARTClass Serial4( USART3, USART3_IRQn, ID_USART3, &rx_buffer4 ) ;
 
 // IT handlers
 void USART0_Handler( void )
@@ -303,7 +303,7 @@ void USART1_Handler( void )
   Serial3.IrqHandler() ;
 }
 
-void USART2_Handler( void )
+void USART3_Handler( void )
 {
   Serial4.IrqHandler() ;
 }