--- /dev/null
+diff --git a/src/curvature.c b/src/curvature.c
+index 70f6af2..a5c0187 100644
+--- a/src/curvature.c
++++ b/src/curvature.c
+@@ -17,6 +17,9 @@
+ * Boston, MA 02111-1307, USA.
+ */
+
++#ifdef _WIN32
++#define _USE_MATH_DEFINES
++#endif
+ #include <math.h>
+ #include "gts.h"
+
+diff --git a/src/triangle.c b/src/triangle.c
+index 1d82869..47170c6 100644
+--- a/src/triangle.c
++++ b/src/triangle.c
+@@ -17,6 +17,9 @@
+ * Boston, MA 02111-1307, USA.
+ */
+
++#ifdef _WIN32
++#define _USE_MATH_DEFINES
++#endif
+ #include <math.h>
+ #include "gts.h"
+