Irrespective of which is correct, your post reminded me of the story about the chap who was given too much change by a shopkeeper. As he was walking away down the street the shopkeeper came running after him shouting that he'd given the wrong change. The customer pointed to the sign in the window and said something along the lines of "tufftitty".
Both are obviously acceptable, though the single word is much more prevalent. I would only separate them in circumstances in which I wanted to stress the negative aspect. In other words, if saying, in effect, "Don't even bloody THINK of trying to get a mistake rectified!"