next.js/examples/with-glamor/next.config.js

const webpack = require('webpack')

module.exports = {
  webpack: (config, { buildId, dev, isServer, defaultLoaders }) => {
    const { plugins } = config
    return {
      ...config,
      plugins: [
        ...(plugins || []),
        new webpack.ProvidePlugin({
          Glamor: 'glamor/react'
        })
      ]
    }
  }
}