diff --git a/libraries/AP_HAL_AVR/HAL_AVR_APM1_Class.cpp b/libraries/AP_HAL_AVR/HAL_AVR_APM1_Class.cpp
index e505d68ce7..29d00ec225 100644
--- a/libraries/AP_HAL_AVR/HAL_AVR_APM1_Class.cpp
+++ b/libraries/AP_HAL_AVR/HAL_AVR_APM1_Class.cpp
@@ -40,6 +40,7 @@ HAL_AVR_APM1::HAL_AVR_APM1() :
         &avrUart0Driver, /* phys UART0 -> uartA */
         &avrUart1Driver, /* phys UART1 -> uartB */
         &avrUart3Driver, /* phys UART3 -> uartC */
+        NULL, /* no uartD */
         &avrI2CDriver,
         &apm1SPIDriver,
         &avrAnalogIn,
diff --git a/libraries/AP_HAL_AVR/HAL_AVR_APM2_Class.cpp b/libraries/AP_HAL_AVR/HAL_AVR_APM2_Class.cpp
index a38d224201..919c6d867c 100644
--- a/libraries/AP_HAL_AVR/HAL_AVR_APM2_Class.cpp
+++ b/libraries/AP_HAL_AVR/HAL_AVR_APM2_Class.cpp
@@ -39,6 +39,7 @@ HAL_AVR_APM2::HAL_AVR_APM2() :
         &avrUart0Driver, /* phys UART0 -> uartA */
         &avrUart1Driver, /* phys UART1 -> uartB */
         &avrUart2Driver, /* phys UART2 -> uartC */
+        NULL,            /* no uartD */
         &avrI2CDriver,
         &apm2SPIDriver,
         &avrAnalogIn,