diff --git a/f3brew.c b/f3brew.c
index 2e9c4d2..b01953a 100644
--- a/f3brew.c
+++ b/f3brew.c
@@ -171,7 +171,7 @@ int main(void)
 			22,		/* Wrap.	*/
 			9,		/* Block order. */
 			false)		/* Keep file?	*/
-		: create_block_device("/dev/sdc", false);
+		: create_block_device("/dev/sdc", 0, RT_MANUAL_USB);
 	assert(dev);
 
 	write_and_read_blocks(dev, first_block, last_block);
diff --git a/f3probe.c b/f3probe.c
index a59bf51..566a42e 100644
--- a/f3probe.c
+++ b/f3probe.c
@@ -35,14 +35,14 @@ static struct argp_option options[] = {
 		"Fake size of the emulated drive",	0},
 	{"debug-wrap",		'w',	"N",		OPTION_HIDDEN,
 		"Wrap parameter of the emulated drive",	0},
-	{"debug-block-order",	'b',	"ORDER",	OPTION_HIDDEN,
-		"Block size the emulated drive is 2^ORDER Byte",	0},
 	{"debug-keep-file",	'k',	NULL,		OPTION_HIDDEN,
 		"Don't remove file used for emulating the drive",	0},
 	{"debug-unit-test",	'u',	NULL,		OPTION_HIDDEN,
 		"Run a unit test; it ignores all other debug options",	0},
+	{"block-order",		'b',	"ORDER",	0,
+		"Force block size of the drive to 2^ORDER Bytes",	2},
 	{"destructive",		'n',	NULL,		0,
-		"Do not restore blocks of the device after probing it",	2},
+		"Do not restore blocks of the device after probing it",	0},
 	{"min-memory",		'l',	NULL,		0,
 		"Trade speed for less use of memory",		0},
 	{"reset-type",		's',	"TYPE",		0,
@@ -159,9 +159,9 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state)
 
 	case 'b':
 		ll = arg_to_long_long(state, arg);
-		if (ll < 9 || ll > 20)
+		if (ll != 0 && (ll < 9 || ll > 20))
 			argp_error(state,
-				"Block order must be in the interval [9, 20]");
+				"Block order must be in the interval [9, 20] or be zero");
 		args->block_order = ll;
 		args->debug = true;
 		break;
@@ -367,7 +367,8 @@ static int test_device(struct args *args)
 		? create_file_device(args->filename, args->real_size_byte,
 			args->fake_size_byte, args->wrap, args->block_order,
 			args->keep_file)
-		: create_block_device(args->filename, args->reset_type);
+		: create_block_device(args->filename, args->block_order,
+			args->reset_type);
 	if (!dev) {
 		fprintf(stderr, "\nApplication cannot continue, finishing...\n");
 		exit(1);
@@ -480,7 +481,7 @@ int main(int argc, char **argv)
 		.real_size_byte	= 1ULL << 31,
 		.fake_size_byte	= 1ULL << 34,
 		.wrap		= 31,
-		.block_order	= 9,
+		.block_order	= 0,
 	};
 
 	/* Read parameters. */
diff --git a/libdevs.c b/libdevs.c
index 12a4ab5..748d0db 100644
--- a/libdevs.c
+++ b/libdevs.c
@@ -232,9 +232,6 @@ struct device *create_file_device(const char *filename,
 {
 	struct file_device *fdev;
 
-	if (!dev_param_valid(real_size_byte, fake_size_byte, wrap, block_order))
-		goto error;
-
 	fdev = malloc(sizeof(*fdev));
 	if (!fdev)
 		goto error;
@@ -251,6 +248,18 @@ struct device *create_file_device(const char *filename,
 		assert(!unlink(filename));
 	}
 
+	if (!block_order) {
+		struct stat fd_stat;
+		blksize_t block_size;
+		assert(!fstat(fdev->fd, &fd_stat));
+		block_size = fd_stat.st_blksize;
+		block_order = ilog2(block_size);
+		assert(block_size == (1 << block_order));
+	}
+
+	if (!dev_param_valid(real_size_byte, fake_size_byte, wrap, block_order))
+		goto keep_file;
+
 	fdev->real_size_byte = real_size_byte;
 	fdev->address_mask = (((uint64_t)1) << wrap) - 1;
 
@@ -263,6 +272,10 @@ struct device *create_file_device(const char *filename,
 
 	return &fdev->dev;
 
+keep_file:
+	if (keep_file)
+		unlink(filename);
+	assert(!close(fdev->fd));
 fdev:
 	free(fdev);
 error:
@@ -562,13 +575,13 @@ static struct udev_device *map_partition_to_disk(struct udev_device *dev)
 	return udev_device_ref(disk_dev);
 }
 
-struct device *create_block_device(const char *filename, enum reset_type rt)
+struct device *create_block_device(const char *filename, int block_order,
+	enum reset_type rt)
 {
 	struct block_device *bdev;
 	struct udev *udev;
 	struct udev_device *fd_dev, *usb_dev;
 	const char *s;
-	int block_size;
 
 	bdev = malloc(sizeof(*bdev));
 	if (!bdev)
@@ -648,9 +661,13 @@ struct device *create_block_device(const char *filename, enum reset_type rt)
 
 	assert(!ioctl(bdev->fd, BLKGETSIZE64, &bdev->dev.size_byte));
 
-	assert(!ioctl(bdev->fd, BLKBSZGET, &block_size));
-	bdev->dev.block_order = ilog2(block_size);
-	assert(block_size == (1 << bdev->dev.block_order));
+	if (!block_order) {
+		int block_size;
+		assert(!ioctl(bdev->fd, BLKBSZGET, &block_size));
+		block_order = ilog2(block_size);
+		assert(block_size == (1 << block_order));
+	}
+	bdev->dev.block_order = block_order;
 
 	bdev->dev.read_block = bdev_read_block;
 	bdev->dev.write_block = bdev_write_block;
diff --git a/libdevs.h b/libdevs.h
index 93fbd90..e29db15 100644
--- a/libdevs.h
+++ b/libdevs.h
@@ -74,7 +74,8 @@ enum reset_type {
 };
 #define RT_DEFAULT	RT_MANUAL_USB
 
-struct device *create_block_device(const char *filename, enum reset_type rt);
+struct device *create_block_device(const char *filename, int block_order,
+	enum reset_type rt);
 
 struct device *create_perf_device(struct device *dev);
 void perf_device_sample(struct device *dev,