memcpy(buf, &header, sizeof(header));
 
        // write the buf
-       if ((fd = open(argv[3], O_CREAT|O_WRONLY,0644)) < 0
+       if ((fd = open(argv[3], O_CREAT|O_WRONLY|O_TRUNC,0644)) < 0
        || write(fd, buf, buflen) != buflen
        || close(fd) < 0)
        {
 
                        exit(3);
                } else {
                        // all is well, write the file without the prefix
-                       if ((fd = open(argv[3], O_CREAT|O_WRONLY,0644)) < 0
+                       if ((fd = open(argv[3], O_CREAT|O_WRONLY|O_TRUNC,0644)) < 0
                        || write(fd, trx + sizeof(struct motorola), len - sizeof(struct motorola)) !=  len - sizeof(struct motorola)
                        || close(fd) < 0)
                        {
                firmware->crc = htonl(crc32buf((unsigned char *)&firmware->flags, sizeof(firmware->flags) + len));
 
                // write the firmware
-               if ((fd = open(argv[3], O_CREAT|O_WRONLY,0644)) < 0
+               if ((fd = open(argv[3], O_CREAT|O_WRONLY|O_TRUNC,0644)) < 0
                || write(fd, firmware, sizeof(struct motorola) + len) != sizeof(struct motorola) + len
                || close(fd) < 0)
                {
 
                printf("%ld\n", ((long) len * 512));
        }
 
-       if ((fd = open(filename, O_WRONLY|O_CREAT, 0644)) < 0) {
+       if ((fd = open(filename, O_WRONLY|O_CREAT|O_TRUNC, 0644)) < 0) {
                fprintf(stderr, "Can't open output file '%s'\n",filename);
                return -1;
        }