Non-breaking hyphen in Index entries

[Nancy Allison]

I am being driven mad by a teensy technical question that I KNOW I have solved in the past.

I have document with chapter-page numbering, and an index entry that is a tad long, so it breaks like this:

apple pie, baking at high altitudes, 4-
6

When I go to the correct Reference page, I find the format set up as you would expect:

<$chapnum>-<$pagenum>

I have tried replacing the hyphen with Esc hyphen h and with \+

Neither works!

What am I missing? I know I have done this before.

Many thanks.