diff --git a/usr.sbin/installboot/arch/macppc.c b/usr.sbin/installboot/arch/macppc.c
index d4696b7ed5e8..667757ae7684 100644
--- a/usr.sbin/installboot/arch/macppc.c
+++ b/usr.sbin/installboot/arch/macppc.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: macppc.c,v 1.9 2008/04/28 20:24:16 martin Exp $ */
+/*	$NetBSD: macppc.c,v 1.10 2008/05/09 10:14:35 tsutsui Exp $ */
 
 /*-
  * Copyright (c) 2002 The NetBSD Foundation, Inc.
@@ -35,10 +35,14 @@
 
 #include <sys/cdefs.h>
 #if !defined(__lint)
-__RCSID("$NetBSD: macppc.c,v 1.9 2008/04/28 20:24:16 martin Exp $");
+__RCSID("$NetBSD: macppc.c,v 1.10 2008/05/09 10:14:35 tsutsui Exp $");
 #endif	/* !__lint */
 
 #include <sys/param.h>
+#ifndef HAVE_NBTOOL_CONFIG_H
+#include <sys/ioctl.h>
+#include <sys/dkio.h>
+#endif
 
 #include <assert.h>
 #include <err.h>
@@ -92,6 +96,10 @@ writeapplepartmap(ib_params *params, struct bbinfo_params *bb_params,
 {
 	struct apple_drvr_map dm;
 	struct apple_part_map_entry pme;
+	int rv;
+#ifdef DIOCWLABEL
+	int enable;
+#endif
 
 	assert (params != NULL);
 	assert (bb_params != NULL);
@@ -109,8 +117,27 @@ writeapplepartmap(ib_params *params, struct bbinfo_params *bb_params,
 	dm.sbSig =		htobe16(APPLE_DRVR_MAP_MAGIC);
 	dm.sbBlockSize =	htobe16(512);
 	dm.sbBlkCount =		htobe32(0);
-	if (pwrite(params->fsfd, &dm, MACPPC_BOOT_BLOCK_BLOCKSIZE, 0) !=
-	    MACPPC_BOOT_BLOCK_BLOCKSIZE) {
+
+#ifdef DIOCWLABEL
+	/*
+	 * block 0 is LABELSECTOR which might be protected by
+	 * bounds_check_with_label(9).
+	 */
+	enable = 1;
+	rv = ioctl(params->fsfd, DIOCWLABEL, &enable);
+	if (rv != 0) {
+		warn("Cannot enable writes to the label sector");
+		return 0;
+	}
+#endif
+	rv = pwrite(params->fsfd, &dm, MACPPC_BOOT_BLOCK_BLOCKSIZE, 0);
+
+#ifdef DIOCWLABEL
+	/* Reset write-protect. */
+	enable = 0;
+	(void)ioctl(params->fsfd, DIOCWLABEL, &enable);
+#endif
+	if (rv != MACPPC_BOOT_BLOCK_BLOCKSIZE) {
 		warn("Can't write sector 0 of `%s'", params->filesystem);
 		return (0);
 	}