1 files changed, 3 insertions, 0 deletions
diff --git a/math.c b/math.c
index 5461763d56..e3a78f74e3 100644
--- a/math.c
+++ b/math.c
@@ -51,6 +51,9 @@ extern VALUE rb_to_float(VALUE val);
 static VALUE
 math_atan2(VALUE obj, VALUE y, VALUE x)
 {
+#ifndef M_PI
+# define M_PI 3.14159265358979323846
+#endif
     double dx, dy;
     Need_Float2(y, x);
     dx = RFLOAT_VALUE(x);