|Abstract:||The proper understanding of infixation continues to be a matter of debate among linguists. The data presented in this paper show that infixation in Austronesian languages is not exclusively due to prosodic morphology, but instead is significantly influenced by the segmental phonology as well. Specifically, infixation may be blocked if it would create dissimilation environments in the first bimoraic foot of the morphological base. To capture this asymmetric effect, it is proposed that OCP-type markedness constraints may be sensitive to positional domains. The analysis also accounts for the alternatives to infixation that individual languages employ. Blocking creates a morphological gap in Tagalog. In contrast, infixation in Chamorro competes with prefixation plus metathesis, whereas prefixation with assimilation is observed in Toba Batak. The investigation of Chamorro also uncovers the phonological conspiracy that infixation and metathesis are both driven by the prosodic requirement that syllables must have onsets.