How to access `.or` prop of decoders

I'd like to compose a decoder, something like:

import * as b32 from 'multiformats/bases/base32'
import * as b36 from 'multiformats/bases/base36'
import * as b58 from 'multiformats/bases/base58'
import * as b64 from 'multiformats/bases/base64'
import { base32 } from 'multiformats/bases/base32'

const bases:Record<string, MultibaseCodec<any>> = {
  ...b32,
  ...b36,
  ...b58,
  ...b64
}

const baseDecoder = Object
  .keys(bases)
  .map(key => bases[key].decoder)
  .reduce(
    (acc, curr) => acc.or(curr),  // <--- fails because `.or` is not in the types though it is in the `Decoder` class
    base32.decoder
  )

It's not clear to me how I'm supposed to do this and not upset the type checker, any pointers?

I tried adding .or to the MultibaseDecoder type def but it explodes because elsewhere you need to know if you're being passed a UnibaseDecoder or a CombobaseDecoder to create a ComposedDecoder - I started trying to fix it but it got a little out of hand so I thought I'd ask instead.