diff --git a/freebsd/sbin/dhclient/privsep.c b/freebsd/sbin/dhclient/privsep.c
index 7b68059a..d5198fa2 100644
--- a/freebsd/sbin/dhclient/privsep.c
+++ b/freebsd/sbin/dhclient/privsep.c
@@ -23,6 +23,9 @@ __FBSDID("$FreeBSD$");
 
 #include "dhcpd.h"
 #include "privsep.h"
+#ifdef __rtems__
+#define	SIZE_T_MAX	SIZE_MAX
+#endif /* __rtems__ */
 
 struct buf *
 buf_open(size_t len)