Sinon stub functions that are exported through an index file

Consider the following typescript files:

• A.ts

export const funcA = ()=>{}

• B.ts

export const funcB = ()=>{}

• index.ts

export * from './A.ts'
export * from './B.ts'

Now in my tests, if I import the inner file directly, I am able to mock its members:

import * as A from './A.ts'
sinon.stub(A,'funcA');

However, if I import the index, it won't let me mock its members:

import * as myModule from `./index.ts`
sinon.stub(myModule,'funcA'); // does not work

Can someone explain? Is there a different approach?