diff --git a/libraries/AP_HAL_AVR/AP_HAL_AVR.cpp b/libraries/AP_HAL_AVR/AP_HAL_AVR.cpp
index 97f60bb24d..96555d5105 100644
--- a/libraries/AP_HAL_AVR/AP_HAL_AVR.cpp
+++ b/libraries/AP_HAL_AVR/AP_HAL_AVR.cpp
@@ -28,7 +28,6 @@ static AVRUARTDriverInstance(avrUart0Driver, 0);
 static AVRUARTDriverInstance(avrUart1Driver, 1);
 static AVRUARTDriverInstance(avrUart2Driver, 2);
 static AVRUARTDriverInstance(avrUart3Driver, 3);
-static EmptyUARTDriver  emptyUartDriver;
 
 static AVRI2CDriver     avrI2CDriver;
 static APM1SPIDeviceManager apm1SPIDriver;
@@ -45,11 +44,11 @@ static APM1RCOutput     apm1RCOutput;
 static APM2RCOutput     apm2RCOutput;
 static AVRScheduler     avrScheduler;
 
+/* On APM1 the physical UART2 is used for SPI. */
 const HAL_AVR AP_HAL_AVR_APM1(
-        (UARTDriver*) &avrUart0Driver,
-        (UARTDriver*) &avrUart1Driver,
-        (UARTDriver*) &emptyUartDriver,
-        (UARTDriver*) &avrUart3Driver,
+        (UARTDriver*) &avrUart0Driver, /* phys UART0 -> uartA */
+        (UARTDriver*) &avrUart1Driver, /* phys UART1 -> uartB */
+        (UARTDriver*) &avrUart3Driver, /* phys UART3 -> uartC */
         &avrI2CDriver,
         &apm1SPIDriver,
         &avrAnalogIn,
@@ -61,11 +60,11 @@ const HAL_AVR AP_HAL_AVR_APM1(
         &apm1RCOutput,
         &avrScheduler );
 
+/* On APM1 the physical UART3 is used for SPI. */
 const HAL_AVR AP_HAL_AVR_APM2(
         (UARTDriver*) &avrUart0Driver,
         (UARTDriver*) &avrUart1Driver,
         (UARTDriver*) &avrUart2Driver,
-        (UARTDriver*) &emptyUartDriver,
         &avrI2CDriver,
         &apm2SPIDriver,
         &avrAnalogIn,
diff --git a/libraries/AP_HAL_AVR/HAL_AVR.cpp b/libraries/AP_HAL_AVR/HAL_AVR.cpp
index 70565facd6..21ecc4b99d 100644
--- a/libraries/AP_HAL_AVR/HAL_AVR.cpp
+++ b/libraries/AP_HAL_AVR/HAL_AVR.cpp
@@ -6,10 +6,10 @@ void HAL_AVR::init(void* opts) const {
 
     scheduler->init((void*)&isr_registry);
    
-    /* uart0 is the serial port used for the console, so lets make sure
+    /* uartA is the serial port used for the console, so lets make sure
      * it is initialized at boot */
-    uart0->begin(115200);
-    console->init((void*)uart0);
+    uartA->begin(115200);
+    console->init((void*)uartA);
     /* The AVR RCInput drivers take an AP_HAL_AVR::ISRRegistry*
      * as the init argument */
     rcin->init((void*)&isr_registry);
diff --git a/libraries/AP_HAL_AVR/HAL_AVR.h b/libraries/AP_HAL_AVR/HAL_AVR.h
index 296b7cd062..49e8e4f7f2 100644
--- a/libraries/AP_HAL_AVR/HAL_AVR.h
+++ b/libraries/AP_HAL_AVR/HAL_AVR.h
@@ -14,10 +14,9 @@
 class AP_HAL_AVR::HAL_AVR : public AP_HAL::HAL {
 public:
     HAL_AVR(
-        AP_HAL::UARTDriver* _uart0,
-        AP_HAL::UARTDriver* _uart1,
-        AP_HAL::UARTDriver* _uart2,
-        AP_HAL::UARTDriver* _uart3,
+        AP_HAL::UARTDriver* _uartA,
+        AP_HAL::UARTDriver* _uartB,
+        AP_HAL::UARTDriver* _uartC,
         AP_HAL::I2CDriver*  _i2c,
         AP_HAL::SPIDeviceManager*  _spi,
         AP_HAL::AnalogIn*   _analogin,
@@ -28,7 +27,7 @@ public:
         AP_HAL::RCInput*    _rcin,
         AP_HAL::RCOutput*   _rcout,
         AP_HAL::Scheduler*  _scheduler)
-        : AP_HAL::HAL(  _uart0, _uart1, _uart2, _uart3,
+        : AP_HAL::HAL(  _uartA, _uartB, _uartC,
                         _i2c, _spi, _analogin, _storage,
                         _dataflash, _console, _gpio, _rcin,
                         _rcout, _scheduler) {}