Index: sbin/geom/class/part/geom_part.c
===================================================================
--- sbin/geom/class/part/geom_part.c
+++ sbin/geom/class/part/geom_part.c
@@ -87,7 +87,7 @@
 static void gpart_show_geom(struct ggeom *, const char *, int);
 static int gpart_show_hasopt(struct gctl_req *, const char *, const char *);
 static void gpart_write_partcode(struct ggeom *, int, void *, ssize_t);
-static void gpart_write_partcode_vtoc8(struct ggeom *, int, void *);
+static void gpart_write_partcode_vtoc8(struct ggeom *, int, void *, ssize_t);
 static void gpart_print_error(const char *);
 static void gpart_backup(struct gctl_req *, unsigned int);
 static void gpart_restore(struct gctl_req *, unsigned int);
@@ -1145,13 +1145,16 @@
 }
 
 static void
-gpart_write_partcode_vtoc8(struct ggeom *gp, int idx, void *code)
+gpart_write_partcode_vtoc8(struct ggeom *gp, int idx, void *code,
+    ssize_t size)
 {
 	char dsf[128];
 	struct gprovider *pp;
 	const char *s;
 	int installed, fd;
 
+	assert(size == VTOC_BOOTSIZE);
+
 	installed = 0;
 	LIST_FOREACH(pp, &gp->lg_provider, lg_provider) {
 		s = find_provcfg(pp, "index");
@@ -1273,7 +1276,7 @@
 		} else {
 			if (partsize != VTOC_BOOTSIZE)
 				errx(EXIT_FAILURE, "invalid bootcode");
-			gpart_write_partcode_vtoc8(gp, idx, partcode);
+			gpart_write_partcode_vtoc8(gp, idx, partcode, partsize);
 		}
 	} else
 		if (bootcode == NULL)
Index: sbin/geom/class/virstor/geom_virstor.c
===================================================================
--- sbin/geom/class/virstor/geom_virstor.c
+++ sbin/geom/class/virstor/geom_virstor.c
@@ -183,6 +183,7 @@
 		goto out;
 	}
 	bcopy(md, sector, size);
+	bzero(sector + size, sectorsize - size);
 	if (pwrite(fd, sector, sectorsize, mediasize - sectorsize) !=
 	    (ssize_t)sectorsize) {
 		error = errno;
Index: sbin/geom/misc/subr.c
===================================================================
--- sbin/geom/misc/subr.c
+++ sbin/geom/misc/subr.c
@@ -302,6 +302,7 @@
 		goto out;
 	}
 	bcopy(md, sector, size);
+	bzero(sector + size, sectorsize - size);
 	if (pwrite(fd, sector, sectorsize, mediasize - sectorsize) !=
 	    sectorsize) {
 		error = errno;