diff --git a/gtsam/3rdparty/cephes/cephes/mconf.h b/gtsam/3rdparty/cephes/cephes/mconf.h
index 08119ef85..e200b9b03 100644
--- a/gtsam/3rdparty/cephes/cephes/mconf.h
+++ b/gtsam/3rdparty/cephes/cephes/mconf.h
@@ -102,9 +102,15 @@
 #define cephes_isfinite(x) isfinite(x)
 #endif
 
+/* M_PI et al. are not defined in math.h in C99, even with _USE_MATH_DEFINES */
 #if !defined(M_PI)
 #define M_PI 3.14159265358979323846
 #endif
+#ifndef M_PI_2
+#define M_PI_2 1.57079632679489661923 /* pi/2 */
+#define M_1_PI 0.31830988618379067154 /* 1/pi */
+#define M_2_PI 0.63661977236758134308 /* 2/pi */
+#endif
 
 /* Constants needed that are not available in the C standard library */
 #define SCIPY_EULER     0.577215664901532860606512090082402431   /* Euler constant */