Index: sys/kern/subr_trap.c
===================================================================
--- sys/kern/subr_trap.c	(revision 208745)
+++ sys/kern/subr_trap.c	(working copy)
@@ -265,7 +265,7 @@
 {
 	static const char unknown[] = "unknown";
 
-	if (p->p_sysent->sv_syscallnames == NULL)
+	if (p->p_sysent->sv_syscallnames == NULL || code >= p->p_sysent->sv_size )
 		return (unknown);
 	return (p->p_sysent->sv_syscallnames[code]);
 }