Custom \bonusqformat in exam class not level with question text

Question

I am creating a set of problems, with the bonus problems starred with an *, but when I use \bonusqformat to customize the mark, it pushes the text onto a new line. Is there any way to prevent this from happening?

MWE

\documentclass{exam}

\bonusqformat{\thequestion *.}
\begin{document}
\begin{questions}
\bonusquestion This is a question.

\end{questions}
\end{document}

Answer 1

Turns out that because of the default behaviour of \bonusqformat (pointed out by egreg), it is easier to achieve this effect by the following code in the preamble:

\newcommand\bonusquestionlabel{\thequestion{}*.}
\makeatletter
\def\question@number{%
  \if@bonus
    \if@bonusqformat
      \makebox[\hsize][s]{\@bonusquestionformat}\hskip-\labelsep
    \else
      \bonusquestionlabel
    \fi
  \else
    \if@qformat
      \makebox[\hsize][s]{\@questionformat}\hskip-\labelsep
    \else
      \questionlabel
    \fi
  \fi
}
\makeatother

This code redefines the question label for bonus questions and makes a new label for them.

Result from the MWE with the extra code in the preamble