Font-family of automatically generated indexterms

Using markup inside an indexterm like

<indexterm>
<primary>
<function>printf()</function>
</primary>
</indexterm>

the word "printf()" does not appear in fixed font in
the index. It appears there in proportional font like
the normal flow of text, neither in HTML, nor in PDF
output .

It might be nice to have a parameter to select whether
I want to enable the same formatting rules as in the
normal flow of text.