diff --git a/libraries/AP_Math/location.cpp b/libraries/AP_Math/location.cpp
index 9e9bff9aef..758ffffe6b 100644
--- a/libraries/AP_Math/location.cpp
+++ b/libraries/AP_Math/location.cpp
@@ -37,12 +37,15 @@ float longitude_scale(const struct Location &loc)
 {
     static int32_t last_lat;
     static float scale = 1.0;
+#if HAL_CPU_CLASS < HAL_CPU_CLASS_150
+    // don't optimise on faster CPUs. It causes some minor errors on Replay
     if (labs(last_lat - loc.lat) < 100000) {
         // we are within 0.01 degrees (about 1km) of the
         // same latitude. We can avoid the cos() and return
         // the same scale factor.
         return scale;
     }
+#endif
     scale = cosf(loc.lat * 1.0e-7f * DEG_TO_RAD);
     scale = constrain_float(scale, 0.01f, 1.0f);
     last_lat = loc.lat;