diff --git a/skeletons/INTEGER.c b/skeletons/INTEGER.c
index 0331e1b5..a839b32b 100644
--- a/skeletons/INTEGER.c
+++ b/skeletons/INTEGER.c
@@ -3,7 +3,9 @@
  * All rights reserved.
  * Redistribution and modifications are permitted subject to BSD license.
  */
+#ifndef _BSD_SOURCE
 #define _BSD_SOURCE /* for snprintf() on some linux systems  */
+#endif
 #include <stdio.h>
 #include <asn_internal.h>
 #include <INTEGER.h>