accidentals clash

[Atte André Jensen]

As the following great composition of mine shows, I cannot figure out
how to print accidentals for both the c and cis in a chord nicely. The
cancelation sign and the sharp are printed on top of each other...

\score {
    \notes \relative c'' {
        r
        <c! cis!>
        <c! \property Staff.Accidental  \override #'extra-offset =#'(-1 . 5)
cis!>
    }
}

Is there a way to print this nicely?
-- 
peace, love & harmony
Atte