How to fix a stretched out wig?

[DollyKim]

Please give me some non adhesive options to deal with a wig that used to fit but the elastic in the cap has given out and now it slides off the doll’s head.

It’s a Monique short boy haircut and Dollzone Fei (msd) with a cap that hooks to his strings. Both from 2007.

[SetsunaKou]

We've sewn in a small length of elastic to the back nape part.

Basically take a 2" length of elastic (the sewing type) and sew each side down vertically at each side of the wig, taking care to stretch it across, so that it 'pulls' the wig together at the nape part and not just lays flat across. It's got to be 'buckling' the wig in the back to 'elasticize it again. Sort of like human wigs do.