diff --git a/usr.sbin/installboot/installboot.c b/usr.sbin/installboot/installboot.c
index c4e6a7a0e..f3867a9c7 100644
--- a/usr.sbin/installboot/installboot.c
+++ b/usr.sbin/installboot/installboot.c
@@ -245,13 +245,13 @@ main(int argc, char *argv[])
 		mode = O_RDWR;
 	}
 
-	if (minixfs3_is_minix_partition(params->filesystem)) {
+	if (minixfs3_is_minix_partition(params)) {
 		/* Old setups has just 1 sector for bootblock,
 		 * but bootxx_minixfs is ~8Kb, so we require new setups
 		 * to have 32 sectors before the first subpartition.
 		 * This prevents from overwriting FS on old setups.
 		 */
-		if (!minixfs3_has_bootblock_space(params->filesystem)) {
+		if (!minixfs3_has_bootblock_space(params)) {
 			err(1, "No space for bootxx, you should have 32 sectors"
 				" before the first subpartition on %s",
 				params->filesystem);
diff --git a/usr.sbin/installboot/installboot.h b/usr.sbin/installboot/installboot.h
index c66fc2ec9..f12ec8e9b 100644
--- a/usr.sbin/installboot/installboot.h
+++ b/usr.sbin/installboot/installboot.h
@@ -166,8 +166,8 @@ void		install_master(const char *device, char *masterboot, char **guide);
 int		isoption(const char *option, const char *test);
 
 	/* minixfs3.c */
-int minixfs3_is_minix_partition(const char* partition);
-int minixfs3_has_bootblock_space(const char* partition);
+int minixfs3_is_minix_partition(ib_params *params);
+int minixfs3_has_bootblock_space(ib_params *params);
 
 
 	/* machines.c */
@@ -178,9 +178,6 @@ extern struct ib_mach ib_mach_ews4800mips;
 extern struct ib_mach ib_mach_hp300;
 extern struct ib_mach ib_mach_hp700;
 extern struct ib_mach ib_mach_i386;
-#ifdef __minix
-extern struct ib_mach ib_mach_i386;
-#endif
 extern struct ib_mach ib_mach_landisk;
 extern struct ib_mach ib_mach_macppc;
 extern struct ib_mach ib_mach_news68k;
diff --git a/usr.sbin/installboot/minixfs3.c b/usr.sbin/installboot/minixfs3.c
index 1951b89bf..8009e5a89 100644
--- a/usr.sbin/installboot/minixfs3.c
+++ b/usr.sbin/installboot/minixfs3.c
@@ -16,7 +16,14 @@
 
 #define MFS_FIRST_SUBP_OFFSET	32
 
-static int minixfs3_read_mbr(const char* device, char* buf)
+enum {
+	TYPE_BAD,
+	TYPE_PART,
+	TYPE_DISK
+};
+
+static int
+minixfs3_read_mbr(const char* device, char* buf)
 {
 	int fd;
 	int bytes;
@@ -56,30 +63,48 @@ static int minixfs3_read_mbr(const char* device, char* buf)
 	return 0;
 }
 
+static int
+minixfs3_get_dev_type(const char *device, ib_params *params)
+{
+	int len, type;
 
-int minixfs3_is_minix_partition(const char* partition)
+	/*
+	 * Unless the -f flag is given, we expect to be provided with a primary
+	 * partition.  That is, a device name that ends with "pN", N being 0-3.
+	 * If the -f flag is given, we assume that anything else is a whole
+	 * disk.  If we were given a subpartition, it will fail the subsequent
+	 * MBR signature test, so we need not check this explicitly.
+	 */
+	len = strlen(device);
+
+	if (len > 2 && device[len-2] == 'p' &&
+	    (unsigned) (device[len-1] - '0') <= 3) {
+		type = TYPE_PART;
+	} else {
+		type = TYPE_DISK;
+	}
+
+	if (type != TYPE_PART && !(params->flags & IB_FORCE)) {
+		fprintf(stderr, "Wrong device %s, must be /.../cxdyp[0-3]\n",
+			device);
+		return TYPE_BAD;
+	}
+
+	return type;
+}
+
+int
+minixfs3_is_minix_partition(ib_params *params)
 {
 	char buf[DFL_SECSIZE]; /* part table + signature */
-	int name_length = strlen(partition);
 
-	/* partition must be 0-3 */
-	if (atol(&partition[name_length-1]) >= 4) {
-		fprintf(stderr, "Wrong device %s, must be /.../cxdyp[0-3]\n",
-			partition);
+	if (minixfs3_get_dev_type(params->filesystem, params) == TYPE_BAD)
 		return 0;
-	}
-
-	/* it should be partition device, not disk */
-	if (partition[name_length-2] != 'p') {
-		fprintf(stderr, "Wrong device %s, must be /.../cxdyp[0-3]\n",
-			partition);
-		return 0;
-	}
 
 	/* MINIX 3 partition with current scheme *must* have subpartitions,
 	 * thus MBR has signature. minixfs3_read_mbr checks the signature.
 	 */
-	if (minixfs3_read_mbr(partition, buf))
+	if (minixfs3_read_mbr(params->filesystem, buf))
 		return 0;
 	return 1;
 }
@@ -89,52 +114,55 @@ int minixfs3_is_minix_partition(const char* partition)
  * to install bootxx_minixfs3. New installation should have 16Kb before
  * the first subpartition.
  */
-int minixfs3_has_bootblock_space(const char* partition)
+int
+minixfs3_has_bootblock_space(ib_params *params)
 {
+	const char *device;
 	char buf[DFL_SECSIZE]; /* part table + signature */
-	char disk[NAME_MAX];
+	char parent_name[NAME_MAX];
 	struct mbr_partition *part;
 	uint32_t first_subpartition = (uint32_t) ~0;
-	uint32_t parent_partition = 0;
-	int i;
-	int name_length = strlen(partition);
+	uint32_t parent_partition;
+	int i, len, type = 0;
 
-	/* partition must be 0-3 */
-	if (atol(&partition[name_length-1]) >= 4) {
-		fprintf(stderr, "Wrong device %s, must be /.../cxdyp[0-3]\n",
-			partition);
-		exit(1);
-	}
-	/* it should be partition device, not disk */
-	if (partition[name_length-2] != 'p') {
-		fprintf(stderr, "Wrong device %s, must be /.../cxdyp[0-3]\n",
-			partition);
-		exit(1);
-	}
+	device = params->filesystem;
 
-	if (minixfs3_read_mbr(partition, buf))
+	if ((type = minixfs3_get_dev_type(device, params)) == TYPE_BAD)
+		exit(1);
+
+	if (minixfs3_read_mbr(device, buf))
 		exit(1);
 
 	part = (struct mbr_partition *) buf;
 
 	for (i = 0; i < 4; i++) {
-		if (part[i].mbrp_size && part[i].mbrp_start < first_subpartition)
+		if (part[i].mbrp_size &&
+		    part[i].mbrp_start < first_subpartition)
 			first_subpartition = part[i].mbrp_start;
 	}
 
-	strncpy(disk, partition, name_length - 2);
-	disk[name_length - 2] = '\0';
+	if (type == TYPE_PART) {
+		/* The target is a partition.  Look up its starting offset. */
+		len = strlen(device);
+		strncpy(parent_name, device, len - 2);
+		parent_name[len - 2] = '\0';
 
-	if (minixfs3_read_mbr(disk, buf))
-		exit(1);
+		if (minixfs3_read_mbr(parent_name, buf))
+			exit(1);
 
-	for (i = 0; i < 4; i++) {
-		struct mbr_partition *p = &part[i];
-		if (p->mbrp_size && p->mbrp_start <= first_subpartition
-		    && (p->mbrp_start + p->mbrp_size) > first_subpartition) {
-			parent_partition = p->mbrp_start;
-			break;
+		parent_partition = 0;
+		for (i = 0; i < 4; i++) {
+			struct mbr_partition *p = &part[i];
+			if (p->mbrp_size && p->mbrp_start <= first_subpartition
+			    && (p->mbrp_start + p->mbrp_size) >
+			    first_subpartition) {
+				parent_partition = p->mbrp_start;
+				break;
+			}
 		}
+	} else {
+		/* The target is a whole disk.  The starting offset is 0. */
+		parent_partition = 0;
 	}
 
 	if ((first_subpartition - parent_partition) < MFS_FIRST_SUBP_OFFSET)