diff --git a/src/bacnet/lighting.c b/src/bacnet/lighting.c
index 657991dc..af3dc6f7 100644
--- a/src/bacnet/lighting.c
+++ b/src/bacnet/lighting.c
@@ -15,7 +15,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>
-#define __USE_ISOC99
 #include <math.h>
 #include "bacnet/bacdcode.h"
 #include "bacnet/bacreal.h"