By around 12 months, infants have well-specified phonetic representations for the nouns they understand, for instance looking less at a car upon hearing ‘cur’ than ‘car’ (Swingley and Aslin, 2002). Here we test whether such high-fidelity representations extend to irregular nouns, and regular and irregular verbs. A corpus analysis confirms the intuition that irregular verbs are far more common than irregular nouns in speech to young children. Two eyetracking experiments then test whether toddlers are sensitive to mispronunciation in regular and irregular nouns (Experiment 1) and verbs (Experiment 2). For nouns, we find a mispronunciation effect and no regularity effect in 18-month-olds. For verbs, in Experiment 2a, we find only a regularity effect and no mispronunciation effect in 18-month-olds, though toddlers’ poor comprehension overall limits interpretation. Finally, in Experiment 2b we find a mispronunciation effect and no regularity effect in 26-month-olds. The interlocking roles of lexical class and regularity for wordform representations and early word learning are discussed.