How can speech be retimed so as to maximise its intelligibility in the face of competing speech? We present a general strategy which modifies local speech rate to minimise overlap with a known fluctuating masker. Continuous time-scale factors are derived in an optimisation procedure which seeks to minimise overall energetic masking of the speech by the masker while additionally unmasking those speech regions potentially most important for speech recognition. Intelligibility increases are evaluated with both objective and subjective measures and show significant gains over an unmodified baseline, with larger benefits at lower signal-to-noise ratios. The retiming approach does not lead to benefits for speech mixed with stationary maskers, suggesting that the gains observed for the fluctuating masker are not simply due to durational expansion.