Blitting problem

I have set up a DX text engine, but I am having some problems with scaling. What I do is load the entire font bitmap (1 line with 97 characters) to a surface. User enters a string, and it blits the individual characters to another surface. From there, it is blit to a target rect on a target surface, so it using scaling most of the time. The problem is, when I scale, the font becomes garbled. The letters are black, but have some white and greys mixed where the white previously was. Can someone help me out? Thanks