Style issue -- no scroll bar when the page is wider than the screen?

[Merriweather]

I have a style problem where if the post is stretched wider than the layout, instead of actually stretching and giving users a scrollbar, it's just cutting it off. So if a user posts a large image that makes the post extend past the right side of the screen, the report nd other buttons get cut off -- you can't scroll to see them at all.

Has anyone else experienced this, and how did you fix it?