First I made a backup of my /etc/X11/xorg.conf file just in case something got messed up.
Then I edited /etc/X11/xorg.conf and found the “Device” section. I added the following lines below the “Driver” line:
Option “TwinView” “True”
Option “TwinViewOrientation” “RightOf”
Option “UseEdidFreqs” “True”
Option “MetaModes” “1280×1024,1280×1024”
Option “UseDisplayDevice” “CRT,DFP”
The “UseDisplayDevice” line can be tricky. I have two flat panel displays, however only one of them is using the DVI connection. So, instead of having “DFP,DFP”, I have to have “CRT,DFP”. The flat panel display on my left coincides with the CRT because it is connected via the D-Sub and the flat panel on my right is the DFP because it is connected with the DVI.
After I added these lines, I refreshed X windows by pressing <ctl> + <alt> + <backspace>. You can reboot your machine if you would rather.