diff --git a/libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp b/libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp
index 074dd10c7b..8582653c0c 100644
--- a/libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp
+++ b/libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp
@@ -268,7 +268,7 @@ void AC_AttitudeControl_Heli::rate_controller_run()
 // Update Alt_Hold angle maximum
 void AC_AttitudeControl_Heli::update_althold_lean_angle_max(float throttle_in)
 {
-    float althold_lean_angle_max = acos(constrain_float(_throttle_in/AC_ATTITUDE_HELI_ANGLE_LIMIT_THROTTLE_MAX, 0.0f, 1.0f));
+    float althold_lean_angle_max = acosf(constrain_float(_throttle_in/AC_ATTITUDE_HELI_ANGLE_LIMIT_THROTTLE_MAX, 0.0f, 1.0f));
     _althold_lean_angle_max = _althold_lean_angle_max + (_dt/(_dt+_angle_limit_tc))*(althold_lean_angle_max-_althold_lean_angle_max);
 }
 
diff --git a/libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp b/libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp
index 0601800d4d..0d52172470 100644
--- a/libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp
+++ b/libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp
@@ -188,7 +188,7 @@ void AC_AttitudeControl_Multi::update_althold_lean_angle_max(float throttle_in)
         return;
     }
 
-    float althold_lean_angle_max = acos(constrain_float(_throttle_in/(AC_ATTITUDE_CONTROL_ANGLE_LIMIT_THROTTLE_MAX * thr_max), 0.0f, 1.0f));
+    float althold_lean_angle_max = acosf(constrain_float(_throttle_in/(AC_ATTITUDE_CONTROL_ANGLE_LIMIT_THROTTLE_MAX * thr_max), 0.0f, 1.0f));
     _althold_lean_angle_max = _althold_lean_angle_max + (_dt/(_dt+_angle_limit_tc))*(althold_lean_angle_max-_althold_lean_angle_max);
 }
 
diff --git a/libraries/AC_AttitudeControl/AC_AttitudeControl_Sub.cpp b/libraries/AC_AttitudeControl/AC_AttitudeControl_Sub.cpp
index ac1b52a185..020702d324 100644
--- a/libraries/AC_AttitudeControl/AC_AttitudeControl_Sub.cpp
+++ b/libraries/AC_AttitudeControl/AC_AttitudeControl_Sub.cpp
@@ -195,7 +195,7 @@ void AC_AttitudeControl_Sub::update_althold_lean_angle_max(float throttle_in)
         return;
     }
 
-    float althold_lean_angle_max = acos(constrain_float(_throttle_in/(AC_ATTITUDE_CONTROL_ANGLE_LIMIT_THROTTLE_MAX * thr_max), 0.0f, 1.0f));
+    float althold_lean_angle_max = acosf(constrain_float(_throttle_in/(AC_ATTITUDE_CONTROL_ANGLE_LIMIT_THROTTLE_MAX * thr_max), 0.0f, 1.0f));
     _althold_lean_angle_max = _althold_lean_angle_max + (_dt/(_dt+_angle_limit_tc))*(althold_lean_angle_max-_althold_lean_angle_max);
 }