PHPStorm 2020.2 Reports SCSS error on lists using square brackets

PHPStorm is reporting errors in SCSS files when using square bracket list syntax, such as

$list: [5px, 10px, 18px];

It shows an error at the 5, saying "']' expected", and at the closing ] saying "a term expected".

Or similarly when used as an argument to a mixin:

@include my-mixin([h3, h4]) {
    color: red;
}

Shows an error at the comma, "']' expected". And shows an error at "h4]" saying "Invalid argument".