How to add a token to an existing language (e.g. typescript)?

I can define tokens with setMonarchTokensProvider, but that does not really help because I can only make a new language or overwrite typescript. In either case I do not have the rest of the typescript tokens which I still want to have.

I just want to add one token, which will have a specific meaning in the context of this editor, which I want to colorize. While still having all of typescript.

This is what I have till now (taken form the playground examples), but with this the rest of typescript is gone:

monaco.languages.setMonarchTokensProvider('typescript', {
    tokenizer: {
        root: [
            [/\pvm.*/, "custom-error"]
        ]
    }
});


monaco.editor.defineTheme('myCoolTheme', {
    base: 'vs',
    inherit: true,
    rules: [
        { token: 'custom-error', foreground: 'ff0000', fontStyle: 'bold' }
    ]
});

(And then using theme myCoolTheme when creating the editor)