diff --git a/c++/contourgl/geometry.h b/c++/contourgl/geometry.h
index 4df5f39..ea6f4c6 100644
--- a/c++/contourgl/geometry.h
+++ b/c++/contourgl/geometry.h
@@ -23,6 +23,11 @@
 #include <algorithm>
 
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+
 typedef double Real;
 
 template<typename T>