java.time.format.DateTimeParseException for dd-MMM-yy format

I am trying for hours now to parse this String to LocalDate and I just can't find where my pattern is wrong.

 public void parseDate() {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd'-'MMM'-'yy");
        LocalDate date = LocalDate.parse("05-Sep-20", formatter);
}

I get the following exception:

java.time.format.DateTimeParseException: Text '05-Sep-20' could not be parsed at index 3

It works fine when using the pattern dd'-'MMMM'-'yy or dd'-'MM'-'yy, but it just won't work for MMM

I used the single quotes around the dash, because otherwise I was getting a parsing exception at a different index.

I am using Java1.8 and java.time