[NTG-context] Index formatting: column leaks over page margin

I have a tiny problem with the formatting of an index placed with \completeindex. When there are more than 14 or so page numbers for an entry and the entry is in the right hand column, the numbers leak over the page boundary. I haven't done any special formatting for these index pages - is there a command that says keep the columns for a \completeindex less than x cm wide or something?