You might find this is more common than you think. If I prepare a particular sentence to try to avoid stuttering on it, I'll know the word(s) I'll struggle with. The weird thing is, if I feel more important than the person I'm talking to, I'll not stutter at all. Best of luck with your interview. Remember that you're also interviewing them - do you want to work there, are they good enough to have you as an employee?