Demasiado + another adverb

[fglorca]

Is it correct to use another adverb after 'demasiado'?
Example:
Mi amiga habla demasiado rápidamente.

I have heard some natives say:
Mi amiga habla demasiado rápido.

Many thanks.

[poli]

There is nothing wrong with demasiado rapidamente except I don't think anyone uses it. In this case, your friend is right.

[Rusty]

Here's a good explanation (https://www.elcastellano.org/cecilia-monsalve-6).

[fglorca]

Many thanks, guys.