TypeScript: inconsistent factory signature (unable to declare custom dependencies)

I'm customizing mathjs extending its types and methods. In JS I can register a type :

  factory('DateTime', ['typed'], function createDateTime({ typed }: { typed?: any }) {
    typed.addType({
      name: 'DateTime',
      test: (x: any) => x && x.constructor.name === 'DateTime'
    })
    return DateTime
  }),

and then use it as a dependency:

factory('datetime', ['typed', 'DateTime'], function createDateTime({ typed, DateTime }) {}

but in TypeScript it's not possible - I'm getting: Type '"DateTime"' is not assignable to type 'keyof MathJsStatic'.

PS> And BTW creating math object is also quite confusing in TypeScript:

import { create, all, factory } from 'mathjs';
const mathjs = create(all);
mathjs!.import!([ ... ]);