This electrophysiological study asked whether the brain processes grammatical gender violations in casual speech differently than in careful speech. Native speakers of Dutch were presented with utterances that contained adjective–noun pairs in which the adjective was either correctly inflected with a word-final schwa (e.g., een spannende roman, “a suspenseful novel”) or incorrectly uninflected without that schwa (een spannend roman). Consistent with previous findings, the uninflected adjectives elicited an electrical brain response sensitive to syntactic violations when the talker was speaking in a careful manner. When the talker was speaking in a casual manner, this response was absent. A control condition showed electrophysiological responses for carefully as well as casually produced utterances with semantic anomalies, showing that listeners were able to understand the content of both types of utterance. The results suggest that listeners take information about the speaking style of a talker into account when processing the acoustic–phonetic information provided by the speech signal. Absent schwas in casual speech are effectively not grammatical gender violations. These changes in syntactic processing are evidence of contextually driven neural flexibility.