Index: gnumach-1.7+git20160809/kern/mach_clock.c
===================================================================
--- gnumach-1.7+git20160809.orig/kern/mach_clock.c
+++ gnumach-1.7+git20160809/kern/mach_clock.c
@@ -533,7 +533,9 @@ host_adjust_time(host, new_adjustment, o
 	thread_bind(current_thread(), PROCESSOR_NULL);
 #endif	/* NCPUS > 1 */
 
-	*old_adjustment = oadj;
+	/* Allow *old_adjustment to be NULL: see man adjtime(3)  */
+	if (old_adjustment)
+		*old_adjustment = oadj;
 
 	return (KERN_SUCCESS);
 }