[NTG-context] Two hyphens do not give en dash

I installed a new font (Gentium, TrueType). Everything went relatively smoothly except for one thing: When I type -- I really get two hyphens instead of the expected en dash. I have been able to work around this by using UTF regime and typing the en dash into the source file. However, it would be easier to use -- and ---. What should I do? (Yeah, I know, forget it and be happy that the UTF works :) TIA, - Ville