Aspirated stops in Tz'utujil (Mayan; Guatemala) only occur before consonants and word boundaries, contrary to Steriade's (1999) observation that languages often limit aspiration to pre-sonorant position. After presenting a quantitative analysis of the phonetics of Tz'utujil stops (based on archival recordings from Oxlajuuj Keej Maya' Ajtz'iib'), I argue that allophonic aspiration is functionally motivated by the need to preserve place and glottal state contrasts in perceptually weak positions (following e.g. Steriade 2001). This analysis is then formalized in Dispersion Theory (Flemming 1995; Padgett 2001; etc.).