--- src/gpart_cpp.cpp	2021-10-26 22:24:23.000000000 +0300
+++ src/gpart_cpp.cpp	2022-01-24 15:11:39.775657833 +0300
@@ -617,12 +617,12 @@
     // three real roots
     sq = sqrt(qq);
     dxx = acos(rr / (qq * sq)) * (1.0 / 3.0);
     sq *= -2;
     solutions[0] = sq * cos(dxx) - adiv3;
-    solutions[1] = sq * cos(dxx + (2.0 * PI / 3.0)) - adiv3;
-    solutions[2] = sq * cos(dxx - (2.0 * PI / 3.0)) - adiv3;
+    solutions[1] = sq * cos(dxx + (2.0 * M_PI / 3.0)) - adiv3;
+    solutions[2] = sq * cos(dxx - (2.0 * M_PI / 3.0)) - adiv3;
     // now sort and check for within-epsilon equality
     if (solutions[0] > solutions[1]) {
       dxx = solutions[0];
       solutions[0] = solutions[1];
       if (dxx > solutions[2]) {