I usually find that interviewers ask about expected salary on a first interview, but I usually feel uncomfortable discussing such details at an early stage. I feel that low-balling a figure might result in under-selling myself, whereas going too high might lose me the chance of a second interview. I also like time to reflect on my interview experience before vocalising my expectations. I recently realised that in one interview I prefixed my salary figure with a justification, which made me come across as a little desperate and unsure of myself.

Is there a good way to defer such questions until a second interview (assuming I get one, of course) without hurting my chances or weakening my position?