diff --git a/libraries/AP_IMU/AP_IMU_Shim.h b/libraries/AP_IMU/AP_IMU_Shim.h
index df94cd87c9..6995a22b79 100644
--- a/libraries/AP_IMU/AP_IMU_Shim.h
+++ b/libraries/AP_IMU/AP_IMU_Shim.h
@@ -14,8 +14,8 @@ public:
 	/// @name IMU protocol
 	//@{
 	virtual void	init(Start_style style, void (*callback)(unsigned long t)) {}
-	virtual void	init_accel() {};
-	virtual void	init_gyro() {};
+	virtual void	init_accel(void (*callback)(unsigned long t) = delay) {};
+	virtual void	init_gyro(void (*callback)(unsigned long t) = delay) {};
 	virtual bool	update(void) {
 		bool updated = _updated;
 		_updated = false;