diff --git a/include/mathconst.h b/include/mathconst.h
index ee11bcc30..56fef8cdf 100755
--- a/include/mathconst.h
+++ b/include/mathconst.h
@@ -25,5 +25,6 @@
 #define	M_SQRT2		1.41421356237309504880168872420969808
 #define	M_1_SQRT2	0.70710678118654752440084436210484904
 #define	M_EULER		0.57721566490153286060651209008240243
+#define	M_SQRT1_2	0.70710678118654752440084436210484904
 
 #endif /* _MATHCONST_H */