diff --git a/libraries/AP_Math/rotations.h b/libraries/AP_Math/rotations.h
index a4161040fc..d63f4174ba 100644
--- a/libraries/AP_Math/rotations.h
+++ b/libraries/AP_Math/rotations.h
@@ -80,6 +80,9 @@ enum Rotation : uint8_t {
 // maximum rotation that will be used for auto-detection
 #define ROTATION_MAX_AUTO_ROTATION ROTATION_ROLL_90_PITCH_315
 
+// definitions used by quaterion and vector3f
+#define HALF_SQRT_2 0.70710678118654757f
+
 /*
 Here are the same values in a form suitable for a @Values attribute in
 auto documentation:
diff --git a/libraries/AP_Math/vector3.cpp b/libraries/AP_Math/vector3.cpp
index a23fbfbb10..984f4172c8 100644
--- a/libraries/AP_Math/vector3.cpp
+++ b/libraries/AP_Math/vector3.cpp
@@ -20,8 +20,6 @@
 
 #include "AP_Math.h"
 
-#define HALF_SQRT_2 0.70710678118654757f
-
 // rotate a vector by a standard rotation, attempting
 // to use the minimum number of floating point operations
 template <typename T>