The prevalence of formulaicity in naturally occurring language use points to an important role in the way language is acquired, processed, and used. It is widely recommended that second-language instruction should ensure that learners develop a rich repertoire of formulaic sequences. If this is justified, it follows that learner failure to use formulaic sequences should present some barrier to communication. However, it seems that few researchers have sought to objectively evaluate how learner deviations from the target-language (formulaic or otherwise) impact on online processing. Operationalizing formulaic sequence through collocation, this article reports the combination of corpus-based approaches and psycholinguistic experimentation to investigate the processing by native speakers of learner collocations that deviate from target-language norms. Results show that such deviations are associated with an increased and sustained processing burden. These findings support the widely asserted claim that formulaic sequences offer processing advantages and provide empirical support for the importance of formulaic sequences in language learning. Usage-based models form the basis for some hypotheses concerning cognitive processes that underlie the increase in processing demands.