diff --git a/libraries/AC_AttitudeControl/AC_AttitudeControl.h b/libraries/AC_AttitudeControl/AC_AttitudeControl.h
index 85f94ff8ed..aa1942bad6 100644
--- a/libraries/AC_AttitudeControl/AC_AttitudeControl.h
+++ b/libraries/AC_AttitudeControl/AC_AttitudeControl.h
@@ -142,7 +142,7 @@ public:
     //
 
     // lean_angle_max - maximum lean angle of the copter in centi-degrees
-    int16_t lean_angle_max() { return _aparm.angle_max; }
+    int16_t lean_angle_max() const { return _aparm.angle_max; }
 
     // user settable parameters
     static const struct AP_Param::GroupInfo var_info[];