We investigate whether there is a within-speaker effect of a higher F0 on the values of the first and the second formant. When asked to speak at a high F0, speakers turn out to raise their formants as well. In the F1 dimension this effect is greater for women than for men. We conclude that while a general formant raising effect might be due to the physiology of a high F0 (i.e. raised larynx and shorter vocal tract), a plausible explanation for the gender-dependent size of the effect can only be found in the undersampling hypothesis.