diff --git a/libraries/APM_RC/APM_RC.h b/libraries/APM_RC/APM_RC.h
index d36b0f11eb..65e5b278d5 100644
--- a/libraries/APM_RC/APM_RC.h
+++ b/libraries/APM_RC/APM_RC.h
@@ -39,7 +39,7 @@ class Arduino_Mega_ISR_Registry;
 class APM_RC_Class
 {
   public:
-	virtual void Init( Arduino_Mega_ISR_Registry * isr_reg );
+	virtual void Init( Arduino_Mega_ISR_Registry * isr_reg ) = 0;
 	virtual void OutputCh(uint8_t ch, uint16_t pwm) = 0;
 	virtual uint16_t InputCh(uint8_t ch) = 0;
 	virtual uint8_t GetState() = 0;