Index: head/lib/geom/part/geom_part.c
===================================================================
--- head/lib/geom/part/geom_part.c
+++ head/lib/geom/part/geom_part.c
@@ -72,6 +72,7 @@
 #define	GPART_PARAM_BOOTCODE	"bootcode"
 #define	GPART_PARAM_INDEX	"index"
 #define	GPART_PARAM_PARTCODE	"partcode"
+#define	GPART_PARAM_SKIP_DSN	"skip_dsn"
 
 static struct gclass *find_class(struct gmesh *, const char *);
 static struct ggeom * find_geom(struct gclass *, const char *);
@@ -115,8 +116,9 @@
 		{ 'p', GPART_PARAM_PARTCODE, G_VAL_OPTIONAL, G_TYPE_STRING },
 		{ 'i', GPART_PARAM_INDEX, G_VAL_OPTIONAL, G_TYPE_NUMBER },
 		{ 'f', "flags", GPART_FLAGS, G_TYPE_STRING },
+		{ 'N', GPART_PARAM_SKIP_DSN, NULL, G_TYPE_BOOL },
 		G_OPT_SENTINEL },
-	    "[-b bootcode] [-p partcode -i index] [-f flags] geom"
+	    "[-N] [-b bootcode] [-p partcode -i index] [-f flags] geom"
 	},
 	{ "commit", 0, gpart_issue, G_NULL_OPTS,
 	    "geom"
Index: head/lib/geom/part/gpart.8
===================================================================
--- head/lib/geom/part/gpart.8
+++ head/lib/geom/part/gpart.8
@@ -49,6 +49,7 @@
 .\" ==== BOOTCODE ====
 .Nm
 .Cm bootcode
+.Op Fl N
 .Op Fl b Ar bootcode
 .Op Fl p Ar partcode Fl i Ar index
 .Op Fl f Ar flags
@@ -214,6 +215,14 @@
 .Cm bootcode
 command accepts these options:
 .Bl -tag -width 10n
+.It Fl N
+Don't preserve the Volume Serial Number for MBR.
+MBR bootcode contains Volume Serial Number by default, and
+.Nm
+tries to preserve it when installing new bootstrap code.
+This option allows to skip the preservation to help with some versions of
+.Xr boot0 8
+that don't support Volume Serial Number.
 .It Fl b Ar bootcode
 Embed bootstrap code from the file
 .Ar bootcode
Index: head/sys/geom/part/g_part.h
===================================================================
--- head/sys/geom/part/g_part.h
+++ head/sys/geom/part/g_part.h
@@ -202,6 +202,7 @@
 #define	G_PART_PARM_BOOTCODE	0x1000
 #define	G_PART_PARM_ATTRIB	0x2000
 #define	G_PART_PARM_FORCE	0x4000
+#define G_PART_PARM_SKIP_DSN	0x8000
 
 struct g_part_parms {
 	unsigned int	gpp_parms;
@@ -220,6 +221,7 @@
 	unsigned int	gpp_codesize;
 	const char	*gpp_attrib;
 	unsigned int	gpp_force;
+	unsigned int	gpp_skip_dsn;
 };
 
 void g_part_geometry_heads(off_t, u_int, off_t *, u_int *);
Index: head/sys/geom/part/g_part.c
===================================================================
--- head/sys/geom/part/g_part.c
+++ head/sys/geom/part/g_part.c
@@ -1627,6 +1627,7 @@
 		if (!strcmp(verb, "bootcode")) {
 			ctlreq = G_PART_CTL_BOOTCODE;
 			mparms |= G_PART_PARM_GEOM | G_PART_PARM_BOOTCODE;
+			oparms |= G_PART_PARM_SKIP_DSN;
 		}
 		break;
 	case 'c':
@@ -1744,6 +1745,8 @@
 				parm = G_PART_PARM_SIZE;
 			else if (!strcmp(ap->name, "start"))
 				parm = G_PART_PARM_START;
+			else if (!strcmp(ap->name, "skip_dsn"))
+				parm = G_PART_PARM_SKIP_DSN;
 			break;
 		case 't':
 			if (!strcmp(ap->name, "type"))
@@ -1803,6 +1806,10 @@
 			break;
 		case G_PART_PARM_SIZE:
 			error = g_part_parm_quad(req, ap->name, &gpp.gpp_size);
+			break;
+		case G_PART_PARM_SKIP_DSN:
+			error = g_part_parm_uint32(req, ap->name,
+			    &gpp.gpp_skip_dsn);
 			break;
 		case G_PART_PARM_START:
 			error = g_part_parm_quad(req, ap->name,
Index: head/sys/geom/part/g_part_mbr.c
===================================================================
--- head/sys/geom/part/g_part_mbr.c
+++ head/sys/geom/part/g_part_mbr.c
@@ -274,7 +274,7 @@
 	table = (struct g_part_mbr_table *)basetable;
 	dsn = *(uint32_t *)(table->mbr + DOSDSNOFF);
 	bcopy(gpp->gpp_codeptr, table->mbr, DOSPARTOFF);
-	if (dsn != 0)
+	if (dsn != 0 && !gpp->gpp_skip_dsn)
 		*(uint32_t *)(table->mbr + DOSDSNOFF) = dsn;
 	return (0);
 }
Index: head/usr.sbin/boot0cfg/boot0cfg.c
===================================================================
--- head/usr.sbin/boot0cfg/boot0cfg.c
+++ head/usr.sbin/boot0cfg/boot0cfg.c
@@ -100,7 +100,7 @@
 
 static int geom_class_available(const char *);
 static int read_mbr(const char *, u_int8_t **, int);
-static void write_mbr(const char *, int, u_int8_t *, int);
+static void write_mbr(const char *, int, u_int8_t *, int, int);
 static void display_mbr(u_int8_t *);
 static int boot0version(const u_int8_t *);
 static int boot0bs(const u_int8_t *);
@@ -200,7 +200,7 @@
 
     /* save the existing MBR if we are asked to do so */
     if (fpath)
-	write_mbr(fpath, O_CREAT | O_TRUNC, mbr, mbr_size);
+	write_mbr(fpath, O_CREAT | O_TRUNC, mbr, mbr_size, 0);
 
     /*
      * If we are installing the boot loader, read it from disk and copy the
@@ -256,7 +256,7 @@
     }
     /* write the MBR back to disk */
     if (up)
-	write_mbr(disk, 0, boot0, boot0_size);
+	write_mbr(disk, 0, boot0, boot0_size, vol_id[4] || b0_ver == 1);
 
     /* display the MBR */
     if (v_flag)
@@ -372,7 +372,8 @@
  * Write out the mbr to the specified file.
  */
 static void
-write_mbr(const char *fname, int flags, u_int8_t *mbr, int mbr_size)
+write_mbr(const char *fname, int flags, u_int8_t *mbr, int mbr_size,
+    int disable_dsn)
 {
 	struct gctl_req *grq;
 	const char *errmsg;
@@ -417,6 +418,9 @@
 		gctl_ro_param(grq, "verb", -1, "bootcode");
 		gctl_ro_param(grq, "bootcode", mbr_size, mbr);
 		gctl_ro_param(grq, "flags", -1, "C");
+		if (disable_dsn)
+			gctl_ro_param(grq, "skip_dsn", sizeof(int),
+			    &disable_dsn);
 		errmsg = gctl_issue(grq);
 		if (errmsg != NULL && errmsg[0] != '\0')
 			errx(1, "GEOM_PART: write bootcode to %s failed: %s",