Index: sys/kern/kern_syscalls.c
===================================================================
--- sys/kern/kern_syscalls.c
+++ sys/kern/kern_syscalls.c
@@ -132,6 +132,7 @@
 	    ("dynamic syscall is not protected"));
 	*old_sysent = sysent[*offset];
 	new_sysent->sy_thrcnt = SY_THR_ABSENT;
+	new_sysent->sy_flags = old_sysent->sy_flags;
 	sysent[*offset] = *new_sysent;
 	atomic_store_rel_32(&sysent[*offset].sy_thrcnt, flags);
 	return (0);