diff --git a/libraries/AP_Math/AP_Math.cpp b/libraries/AP_Math/AP_Math.cpp
index 5e31394bc8..19ef964a00 100644
--- a/libraries/AP_Math/AP_Math.cpp
+++ b/libraries/AP_Math/AP_Math.cpp
@@ -38,40 +38,47 @@ float fast_atan(float v)
     return (v*(1.6867629106f + v2*0.4378497304f)/(1.6867633134f + v2));
 }
 
-#define FAST_ATAN2_PIBY2_FLOAT  1.5707963f
-// fast_atan2 - faster version of atan2
-//      126 us on AVR cpu vs 199 for regular atan2
-//      absolute error is < 0.005 radians or 0.28 degrees
-//      origin source: https://gist.github.com/volkansalma/2972237/raw/
-float fast_atan2(float y, float x)
-{
-   if (x == 0.0f) {
-       if (y > 0.0f) {
-           return FAST_ATAN2_PIBY2_FLOAT;
-       }
-       if (y == 0.0f) {
-           return 0.0f;
-       }
-       return -FAST_ATAN2_PIBY2_FLOAT;
-   }
-   float atan;
-   float z = y/x;
-   if (fabs( z ) < 1.0f) {
-       atan = z / (1.0f + 0.28f * z * z);
-       if (x < 0.0f) {
-           if (y < 0.0f) {
-               return atan - PI;
-           }
-           return atan + PI;
-       }
-   } else {
-       atan = FAST_ATAN2_PIBY2_FLOAT - (z / (z * z + 0.28f));
-       if (y < 0.0f) {
-           return atan - PI;
-       }
-   }
-   return atan;
-}
+#if HAL_CPU_CLASS < HAL_CPU_CLASS_75 || CONFIG_HAL_BOARD == HAL_BOARD_AVR_SITL
+    #define FAST_ATAN2_PIBY2_FLOAT  1.5707963f
+    // fast_atan2 - faster version of atan2
+    //      126 us on AVR cpu vs 199 for regular atan2
+    //      absolute error is < 0.005 radians or 0.28 degrees
+    //      origin source: https://gist.github.com/volkansalma/2972237/raw/
+    float fast_atan2(float y, float x)
+    {
+        if (x == 0.0f) {
+            if (y > 0.0f) {
+                return FAST_ATAN2_PIBY2_FLOAT;
+            }
+            if (y == 0.0f) {
+                return 0.0f;
+            }
+            return -FAST_ATAN2_PIBY2_FLOAT;
+        }
+        float atan;
+        float z = y/x;
+        if (fabs( z ) < 1.0f) {
+            atan = z / (1.0f + 0.28f * z * z);
+            if (x < 0.0f) {
+                if (y < 0.0f) {
+                    return atan - PI;
+                }
+                return atan + PI;
+            }
+        } else {
+            atan = FAST_ATAN2_PIBY2_FLOAT - (z / (z * z + 0.28f));
+            if (y < 0.0f) {
+                return atan - PI;
+            }
+        }
+        return atan;
+    }
+#else
+    float fast_atan2(float y, float x)
+    {
+        return atan2f(y,x);
+    }
+#endif
 
 #if ROTATION_COMBINATION_SUPPORT
 // find a rotation that is the combination of two other