Indexing | (vertical bar) in LaTeX output

[Gavin Smith]

The groff manual indexes "\|" which is output in the LaTeX output as

\index[es]{\textbackslash{}"|@\texttt{\textbackslash{}"|}}%

However this leads to an error: 

! Extra }, or forgotten \endgroup.
<recently read> }
                 
l.72   \item \texttt{\textbackslash{}|}}
                                        , 186
? 

es.idx has a line

\indexentry{\textbackslash{}"|hyperindexformat{\@\texttt{\textbackslash{}"|}}}{1

which becomes in es.ind

  \item \texttt{\textbackslash{}|}}, 186


" is supposed to escape the first | but this doesn't work properly.

The only thing I could find is this page from 2014:

https://tex.stackexchange.com/questions/176931/how-to-escape-character-in-index

but this only treats | in the math context.  A commenter there says it
"confuses hyperref".

The "hyperindexformat" texts appears to be something added by hyperref.

Does anybody know (or know where we could ask) how to escape a | character
in an index entry correctly?