Streams order is not respected

When I try to use merge-stream with gulp-concat, the resulting order of concatenated code blocks is different.

const gulp = require('gulp');
const merge = require('merge-stream');
const less = require('gulp-less');
const concat = require('gulp-concat');
const rename = require('gulp-rename');

gulp.task('build', () => {
    const files = ['file1', 'file2', 'file3'];
    const streams = files.map((file) => {
        return gulp.src(`./${file}.less`)
            .pipe(less());
    });
    return merge(...streams)
        .pipe(concat(`merged.css`))
        .pipe(gulp.dest('./result'));
});

[func0der]

https://www.npmjs.com/package/merge2 <– https://www.npmjs.com/package/streamqueue <-- This is mentioned in a gulp cheat sheet: https://github.com/osscafe/gulp-cheetsheet/raw/master/dist/en-js-p2.pdf

[alexanderby]

ordered-read-streams says I’m using not readable streams.