Mindfulness-based interventions (MBIs) have been linked to positive outcomes for a range of psychological and physical health conditions, prompting the need for a high degree of validity and reliability in the measurement of mindfulness. While a number of mindfulness self-report instruments are available with demonstrated psychometric robustness, limited empirical data are available on the extent to which ratings at different time points may be affected by changes in standards of reference that may occur as a result from having completed an MBI. The present study investigated the presence of response shift in a sample of 181 MBI course participants who completed the 37-item Comprehensive Inventory of Mindfulness Experiences (CHIME) during the first and final week of the course. Measurement invariance testing using confirmatory factor analysis investigated invariance of the factor structure (configural invariance), factor loadings (metric invariance), and intercepts (scalar invariance) across the two measurement time points. Lack of scalar invariance indicated evidence of response shift for 4 or possibly 7 of the 37 items. The relatively minor amount of response shift is encouraging for the field of mindfulness measurement, particularly since it has generally been hypothesized that mindfulness is particularly prone to this phenomenon. Further studies using other instruments and techniques to investigate response shift are recommended.