Unsplitting menu bars?

Sometimes I accidentally split a menu bar (like you can split windows) but there doesn’t appear to be any way of collapsing them again or getting rid of the duplicate menu. I’ve tried dragging it over again to collapse like you do with other windows but it doesn’t do anything. Can someone help me out here?

Just hover your mouse over the seam between the two windows, right click, select ‘join areas’, move your mouse over the window you want to disappear, and click. Voila!

Thank you so much. That was driving me crazy!