generated extra space produces invalid CSS

[fogshot]

I am using CSS beautify as part of this package for Sublime Text 3.
I have this code in a SASS file of mine.

.subnav-list {
    &:not(:first-of-type) {
        ...
    }
}

after prettifying it becomes this, which is invalid (note the extra space before first-of-type).

.subnav-list {
    &:not(: first-of-type) {
        ...
    }
}