Overfull hboxes in index

[David Ireland]

Generating the index for a project, I get a lot of "overfull hbox" error
messages.  The words that are causing these errors have all been placed in a
\hyphenation{} section in the preamble, but although this helps in the body
of the text, it doesn't seem to help in the index.  Should I correct the
.idx or .ind files?

Any suggestions gratefully received.

David Ireland