Words that can be used as both noun and verb create regions of syntactic ambiguity that could create processing challenges for listeners. However, acoustic properties, such as duration, differ between noun and verb uses of such words, and listeners may use these differences to facilitate ambiguity processing. In this study, we replaced noun uses of ambiguous words with verb uses to determine whether these manipulations affected the N400 event-related potential, which is associated with semantic violations, or the P600 component, which is associated with syntactic ambiguity. The results suggest that the acoustic differences between noun/verb polysemes mitigate the extent to which these words are perceived as ambiguous, although the results do not indicate whether replacing one with the other produces a meaning violation. Durational differences in noun/verb polysemes may affect their processing in fluent speech.