dev = simple_strtoul(boot_device, &ep, 16);
        stor_dev = usb_stor_get_dev(dev);
-       if (stor_dev->type == DEV_TYPE_UNKNOWN) {
+       if (stor_dev == NULL || stor_dev->type == DEV_TYPE_UNKNOWN) {
                printf("\n** Device %d not available\n", dev);
                return 1;
        }
        if (strncmp(argv[1], "part", 4) == 0) {
                int devno, ok = 0;
                if (argc == 2) {
-                       for (devno = 0; devno < USB_MAX_STOR_DEV; ++devno) {
+                       for (devno = 0; ; ++devno) {
                                stor_dev = usb_stor_get_dev(devno);
+                               if (stor_dev == NULL)
+                                       break;
                                if (stor_dev->type != DEV_TYPE_UNKNOWN) {
                                        ok++;
                                        if (devno)
                } else {
                        devno = simple_strtoul(argv[2], NULL, 16);
                        stor_dev = usb_stor_get_dev(devno);
-                       if (stor_dev->type != DEV_TYPE_UNKNOWN) {
+                       if (stor_dev != NULL &&
+                           stor_dev->type != DEV_TYPE_UNKNOWN) {
                                ok++;
                                debug("print_part of %x\n", devno);
                                print_part(stor_dev);
                if (argc == 3) {
                        int dev = (int)simple_strtoul(argv[2], NULL, 10);
                        printf("\nUSB device %d: ", dev);
-                       if (dev >= USB_MAX_STOR_DEV) {
+                       stor_dev = usb_stor_get_dev(dev);
+                       if (stor_dev == NULL) {
                                printf("unknown device\n");
                                return 1;
                        }
                        printf("\n    Device %d: ", dev);
-                       stor_dev = usb_stor_get_dev(dev);
                        dev_print(stor_dev);
                        if (stor_dev->type == DEV_TYPE_UNKNOWN)
                                return 1;