FullHuman / postcss-purgecss

When using pnpm to install my project's dependencies I'm getting the following error:

internal/modules/cjs/loader.js:651
    throw err;
    ^

Error: Cannot find module 'postcss'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:649:15)
    at Function.Module._load (internal/modules/cjs/loader.js:575:25)
    at Module.require (internal/modules/cjs/loader.js:705:19)
    at require (internal/modules/cjs/helpers.js:14:16)
    at Object.<anonymous> (/Users/nestor/my-project/node_modules/.registry.npmjs.org/@fullhuman/postcss-purgecss/1.1.0/node_modules/@fullhuman/postcss-purgecss/lib/postcss-purgecss.js:6:31)
    at Module._compile (internal/modules/cjs/loader.js:799:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:810:10)
    at Module.load (internal/modules/cjs/loader.js:666:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:606:12)
    at Function.Module._load (internal/modules/cjs/loader.js:598:3)

Installing postcss manually solves the issue but I'm guessing it's due it not being listed a one of the project's dependencies:

postcss-purgecss/src/index.js

Line 4 in 1a6efc9

import postcss from 'postcss'

Missing `postcss` dependency in package.json