diff --git a/libraries/AC_Avoidance/AC_Avoid.cpp b/libraries/AC_Avoidance/AC_Avoid.cpp
index 795d79a321..4e97e0be76 100644
--- a/libraries/AC_Avoidance/AC_Avoid.cpp
+++ b/libraries/AC_Avoidance/AC_Avoid.cpp
@@ -87,7 +87,7 @@ Vector2f AC_Avoid::get_position()
  * Computes the speed such that the stopping distance
  * of the vehicle will be exactly the input distance.
  */
-float AC_Avoid::get_max_speed(const float kP, const float accel_cmss, const float distance)
+float AC_Avoid::get_max_speed(const float kP, const float accel_cmss, const float distance) const
 {
     return AC_AttitudeControl::sqrt_controller(distance, kP, accel_cmss);
 }
@@ -97,7 +97,7 @@ float AC_Avoid::get_max_speed(const float kP, const float accel_cmss, const floa
  *
  * Implementation copied from AC_PosControl.
  */
-float AC_Avoid::get_stopping_distance(const float kP, const float accel_cmss, const float speed)
+float AC_Avoid::get_stopping_distance(const float kP, const float accel_cmss, const float speed) const
 {
     // avoid divide by zero by using current position if the velocity is below 10cm/s, kP is very low or acceleration is zero
     if (kP <= 0.0f || accel_cmss <= 0.0f || is_zero(speed)) {
diff --git a/libraries/AC_Avoidance/AC_Avoid.h b/libraries/AC_Avoidance/AC_Avoid.h
index 9e6f351da4..c383be2351 100644
--- a/libraries/AC_Avoidance/AC_Avoid.h
+++ b/libraries/AC_Avoidance/AC_Avoid.h
@@ -48,17 +48,17 @@ private:
      * Computes the speed such that the stopping distance
      * of the vehicle will be exactly the input distance.
      */
-    float get_max_speed(const float kP, const float accel_cmss, const float distance);
+    float get_max_speed(const float kP, const float accel_cmss, const float distance) const;
 
     /*
      * Computes distance required to stop, given current speed.
      */
-    float get_stopping_distance(const float kP, const float accel_cmss, const float speed);
+    float get_stopping_distance(const float kP, const float accel_cmss, const float speed) const;
 
     /*
      * Gets the fence margin in cm
      */
-    float get_margin() { return _fence.get_margin() * 100.0f; }
+    float get_margin() const { return _fence.get_margin() * 100.0f; }
 
     // external references
     const AP_AHRS& _ahrs;