diff --git a/isisd/include-netbsd/iso.h b/isisd/include-netbsd/iso.h
index 1a80aec..42b9bc8 100644
--- a/isisd/include-netbsd/iso.h
+++ b/isisd/include-netbsd/iso.h
@@ -192,7 +192,7 @@
 #else
 /* user utilities definitions from the iso library */
 
-#ifdef SUNOS_5
+#ifndef HAVE_SYS_CDEFS_H
 #define	__P(x)	x
 #define	__BEGIN_DECLS
 #define	__END_DECLS