diff --git a/libraries/AP_HAL/GPIO.h b/libraries/AP_HAL/GPIO.h
index 921f2329fc..73af3b2c78 100644
--- a/libraries/AP_HAL/GPIO.h
+++ b/libraries/AP_HAL/GPIO.h
@@ -27,6 +27,8 @@ public:
     virtual void    pinMode(uint8_t pin, uint8_t output) = 0;
     virtual uint8_t read(uint8_t pin) = 0;
     virtual void    write(uint8_t pin, uint8_t value) = 0;
+    virtual int8_t  analogPinToDigitalPin(uint8_t pin) = 0;
+
     /* Alternative interface: */
     virtual AP_HAL::DigitalSource* channel(uint16_t n) = 0;
 
diff --git a/libraries/AP_HAL_AVR/GPIO.cpp b/libraries/AP_HAL_AVR/GPIO.cpp
index b916454a91..4ab8b65551 100644
--- a/libraries/AP_HAL_AVR/GPIO.cpp
+++ b/libraries/AP_HAL_AVR/GPIO.cpp
@@ -61,6 +61,11 @@ void AVRGPIO::pinMode(uint8_t pin, uint8_t mode) {
     }
 }
 
+int8_t AVRGPIO::analogPinToDigitalPin(uint8_t pin)
+{
+	return analogInputToDigitalPin(pin);
+}
+
 uint8_t AVRGPIO::read(uint8_t pin) {
     uint8_t bit = digitalPinToBitMask(pin);
     uint8_t port = digitalPinToPort(pin);
diff --git a/libraries/AP_HAL_AVR/GPIO.h b/libraries/AP_HAL_AVR/GPIO.h
index 9e32c159e6..9d5f92bb87 100644
--- a/libraries/AP_HAL_AVR/GPIO.h
+++ b/libraries/AP_HAL_AVR/GPIO.h
@@ -22,6 +22,7 @@ public:
     AVRGPIO() {}
     void    init() {}
     void    pinMode(uint8_t pin, uint8_t output);
+    int8_t  analogPinToDigitalPin(uint8_t pin);
     uint8_t read(uint8_t pin);
     void    write(uint8_t pin, uint8_t value);
     AP_HAL::DigitalSource* channel(uint16_t);
diff --git a/libraries/AP_HAL_Empty/GPIO.cpp b/libraries/AP_HAL_Empty/GPIO.cpp
index 672ca292a5..8669851881 100644
--- a/libraries/AP_HAL_Empty/GPIO.cpp
+++ b/libraries/AP_HAL_Empty/GPIO.cpp
@@ -12,6 +12,11 @@ void EmptyGPIO::init()
 void EmptyGPIO::pinMode(uint8_t pin, uint8_t output)
 {}
 
+int8_t EmptyGPIO::analogPinToDigitalPin(uint8_t pin)
+{
+	return -1;
+}
+
 
 uint8_t EmptyGPIO::read(uint8_t pin) {
     return 0;
diff --git a/libraries/AP_HAL_Empty/GPIO.h b/libraries/AP_HAL_Empty/GPIO.h
index da429d76c3..b8cef62012 100644
--- a/libraries/AP_HAL_Empty/GPIO.h
+++ b/libraries/AP_HAL_Empty/GPIO.h
@@ -9,6 +9,7 @@ public:
     EmptyGPIO();
     void    init();
     void    pinMode(uint8_t pin, uint8_t output);
+    int8_t  analogPinToDigitalPin(uint8_t pin);
     uint8_t read(uint8_t pin);
     void    write(uint8_t pin, uint8_t value);
 
diff --git a/libraries/AP_HAL_SMACCM/GPIO.cpp b/libraries/AP_HAL_SMACCM/GPIO.cpp
index 6fc2b23558..2c77bfb534 100644
--- a/libraries/AP_HAL_SMACCM/GPIO.cpp
+++ b/libraries/AP_HAL_SMACCM/GPIO.cpp
@@ -15,6 +15,11 @@ void SMACCMGPIO::pinMode(uint8_t pin, uint8_t output)
 {
 }
 
+int8_t SMACCMGPIO::analogPinToDigitalPin(uint8_t pin)
+{
+	return -1;
+}
+
 uint8_t SMACCMGPIO::read(uint8_t pin)
 {
   return 0;
diff --git a/libraries/AP_HAL_SMACCM/GPIO.h b/libraries/AP_HAL_SMACCM/GPIO.h
index 570b145255..0d7367910a 100644
--- a/libraries/AP_HAL_SMACCM/GPIO.h
+++ b/libraries/AP_HAL_SMACCM/GPIO.h
@@ -9,6 +9,7 @@ public:
     SMACCMGPIO();
     void    init();
     void    pinMode(uint8_t pin, uint8_t output);
+    int8_t  analogPinToDigitalPin(uint8_t pin);
     uint8_t read(uint8_t pin);
     void    write(uint8_t pin, uint8_t value);