b.uint32(uint32max) // compressed size
			b.uint32(uint32max) // uncompressed size

			// append a zip64 extra block to Extra
			var buf [28]byte // 2x uint16 + 3x uint64
			eb := writeBuf(buf[:])
			eb.uint16(zip64ExtraID)
			eb.uint16(24) // size = 3x uint64
			eb.uint64(h.UncompressedSize64)
			eb.uint64(h.CompressedSize64)
			eb.uint64(h.offset)
			h.Extra = append(h.Extra, buf[:]...)
		} else {