The inside window is clear plastic / vinyl and zips closed. One day the canvas must have been wonky or something, and someone (not me!) forced the zipper. Where it is stitched (which is like perforated line) it ripped. It's not much of a hardship because when the window is zipped shut except for that one corner, rain doesn't get in, and we could call it 'ventilation', but I'd like to do something to prevent it from getting worse. It's a matter of putting the vinyl back to one piece then attaching it to the zipper, which I could restitch. I'm thinking strong packing tape? Or what about Gorilla glue? Any ideas?