Two studies explored whether perfectionism moderates the impact of implementation intentions on goal progress. Study 1 used an implementation intention manipulation to examine the effects of these plans in interaction with perfectionism on the progress of New Year's resolutions. Study 2 added a repeated implementation intention condition and monitored affect and monthly goal progress. The results of both studies revealed a significant backfire effect of the implementation intentions on goal progress for participants high on a particular dimension of perfectionism (socially prescribed perfectionism). These perfectionists reported doing significantly worse at reaching their personal goals when they were asked to formulate implementation intentions than when they completed a control exercise. There also was evidence that implementation planning aroused negative affect for socially prescribed perfectionists. These results are the first to suggest that implementation planning may be contra-indicated for individuals with self-critical tendencies.