diff --git a/src/main.cpp b/src/main.cpp
index 0c6a509..c50e39c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -141,11 +141,11 @@ struct Sequences
 inline std::array<double, 2> cheap_ruler_k(double latitude)
 {
     // https://github.com/cubao/headers/blob/8ed287a7a1e2a5cd221271b19611ba4a3f33d15c/include/cubao/crs_transform.hpp#L212
-    static constexpr double M_PI = 3.14159265358979323846;
+    static constexpr double PI = 3.14159265358979323846;
     static constexpr double RE = 6378.137;
     static constexpr double FE = 1.0 / 298.257223563;
     static constexpr double E2 = FE * (2 - FE);
-    static constexpr double RAD = M_PI / 180.0;
+    static constexpr double RAD = PI / 180.0;
     static constexpr double MUL = RAD * RE * 1000.;
     double coslat = std::cos(latitude * RAD);
     double w2 = 1.0 / (1.0 - E2 * (1.0 - coslat * coslat));