The avoidance of regular but not irregular plurals inside compounds (e.g., *rats eater vs. mice eater) has been one of the most widely studied morphological phenomena in the psycholinguistics literature. To examine whether the constraints that are responsible for this contrast have any general significance beyond compounding, we investigated derived word forms containing regular and irregular plurals in two experiments. Experiment 1 was an offline acceptability judgment task, and Experiment 2 measured eye movements during reading derived words containing regular and irregular plurals and uninflected base nouns. The results from both experiments show that the constraint against regular plurals inside compounds generalizes to derived words. We argue that this constraint cannot be reduced to phonological properties, but is instead morphological in nature. The eye-movement data provide detailed information on the time-course of processing derived word forms indicating that early stages of processing are affected by a general constraint that disallows inflected words from feeding derivational processes, and that the more specific constraint against regular plurals comes in at a subsequent later stage of processing. We argue that these results are consistent with stage-based models of language processing.Morphological systems are constrained in how inflectional, derivational, and compounding processes may interact with each other. There is, for example, a general tendency for inflectional suffixes to attach outside derivational ones, which is captured by Greenberg's (1966, p. 93) Universal 28: 'If both the derivation and inflection follow the root, or they both precede the root, the derivation is always between the root and the inflection' . Thus in English, forms such as ducklings with the plural suffix appearing after the derivational suffix are grammatically well-formed but not forms with the reverse order (*ducksling).Linguists have analyzed the interaction between different morphological processes in terms of affix-specific selectional restrictions (see e.g., Fabb, 1988;Plag, 1996Plag, , 1999Plag, , 2002 and other kinds of more general constraints (of a semantic,