ExtraSelection with underline not visible

TextEdit::TextEdit()
{
    insertPlainText("hello");

    // Cursor selecting first line
    QTextCursor cursor = textCursor();
    cursor.setPosition(0);
    cursor.movePosition(QTextCursor::EndOfLine, QTextCursor::KeepAnchor);

    // ExtraSelection with underline style
    QTextEdit::ExtraSelection selection;
    selection.format.setUnderlineStyle(QTextCharFormat::SingleUnderline);
    selection.cursor = cursor;

    setExtraSelections(QList<QTextEdit::ExtraSelection>() << selection);
}