Can't change my external hard drive's icon

I actually know how to change the icon and I have done it many times before. But this time I made a small misstep (dragging a picture to the icon to the "get info" page instead of copying and pasting it as usual). Now my icon is all jacked up. The picture is still the default icon but now it has a black background and small white pixels scattered around. I tried using command x to erase it to default and pasting the desired picture but it ended up pasting the same jacked out icon, no matter what image I use. How can fix this?