diff --git a/libraries/AP_Math/quaternion.cpp b/libraries/AP_Math/quaternion.cpp
index 5b25e5dc74..1456c6d3d5 100644
--- a/libraries/AP_Math/quaternion.cpp
+++ b/libraries/AP_Math/quaternion.cpp
@@ -157,7 +157,7 @@ void Quaternion::from_axis_angle(const Vector3f &axis, float theta) {
     }
     float st2 = sinf(theta/2.0f);
 
-    q1 = cos(theta/2.0f);
+    q1 = cosf(theta/2.0f);
     q2 = axis.x * st2;
     q3 = axis.y * st2;
     q4 = axis.z * st2;