diff -u a/lp_lib.h b/lp_lib.h
--- a/lp_lib.h	2016-05-04 19:45:15.753143720 +0900
+++ b/lp_lib.h	2016-05-04 19:53:59.536920722 +0900
@@ -59,9 +59,6 @@
 # if defined _WIN32 && !defined __GNUC__
 #  define isnan _isnan
 # endif
-#if defined NOISNAN
-# define isnan(x) FALSE
-#endif
 
 #define SETMASK(variable, mask)     variable |= mask
 #define CLEARMASK(variable, mask)   variable &= ~(mask)