diff --git a/libraries/AP_HAL_AVR/GPIO.cpp b/libraries/AP_HAL_AVR/GPIO.cpp
index 3b0fa1f2a59..edad1c540b7 100644
--- a/libraries/AP_HAL_AVR/GPIO.cpp
+++ b/libraries/AP_HAL_AVR/GPIO.cpp
@@ -92,7 +92,8 @@ void AVRGPIO::write(uint8_t pin, uint8_t value) {
 
 /* Implement GPIO Interrupt 6, used for MPU6000 data ready on APM2. */
 bool AVRGPIO::attach_interrupt(
-        int interrupt_num, AP_HAL::Proc proc, int mode) {
+        uint8_t interrupt_num, AP_HAL::Proc proc, uint8_t mode) {
+    if (!((mode == 0)||(mode == 1))) return false;
     if (interrupt_num == 6) {
         _interrupt_6 = proc;
         EICRB = (EICRB & ~((1 << ISC60) | (1 << ISC61))) | (mode << ISC60);
@@ -104,7 +105,7 @@ bool AVRGPIO::attach_interrupt(
 }
 
 
-AP_HAL::DigitalSource* AVRGPIO::channel(int pin) {
+AP_HAL::DigitalSource* AVRGPIO::channel(uint16_t pin) {
     uint8_t bit = digitalPinToBitMask(pin);
     uint8_t port = digitalPinToPort(pin);
     if (port == NOT_A_PIN) return NULL;
diff --git a/libraries/AP_HAL_AVR/GPIO.h b/libraries/AP_HAL_AVR/GPIO.h
index 5c94ad0988b..9e32c159e64 100644
--- a/libraries/AP_HAL_AVR/GPIO.h
+++ b/libraries/AP_HAL_AVR/GPIO.h
@@ -24,8 +24,9 @@ public:
     void    pinMode(uint8_t pin, uint8_t output);
     uint8_t read(uint8_t pin);
     void    write(uint8_t pin, uint8_t value);
-    AP_HAL::DigitalSource* channel(int);
-    bool    attach_interrupt(int interrupt_num, AP_HAL::Proc proc, int mode);
+    AP_HAL::DigitalSource* channel(uint16_t);
+    bool    attach_interrupt(uint8_t interrupt_num, AP_HAL::Proc proc,
+            uint8_t mode);
 /* private-ish: only to be used from the appropriate interrupt */
     static AP_HAL::Proc _interrupt_6;
 };