We explored 12-month-olds' flexibility in accepting phonotactically illegal or ill-formed word forms in a modified associative-learning task. Sixty-four English-learning infants were presented with a training phase that either clarified the purpose of a sound--object association task or left the task ambiguous. Infants were then habituated to sets of Czech words with onsets that are illegal in English (e.g., ptak), consonantal sounds (e.g., /l/), or novel functionlike words (e.g., iv). When infants were provided with a training phase that highlighted the purpose of the task, they associated the phonotactically illegal Czech words, but not the consonantal sounds or novel functionlike words, with objects. Thus, English-learning 12-month-old infants' flexibility in associating various sound forms with novel objects is limited to labels that share the structural shape of well-formed nounlike words.