Multilingual models have demonstrated impressive cross-lingual transfer performance. However, test sets like XNLI are monolingual at the example level. In multilingual communities, it is common for polyglots to code-mix when conversing with each other. Inspired by this phenomenon, we present two strong blackbox adversarial attacks (one word-level, one phrase-level) for multilingual models that push their ability to handle code-mixed sentences to the limit. The former uses bilingual dictionaries to propose perturbations and translations of the clean example for sense disambiguation. The latter directly aligns the clean example with its translations before extracting phrases as perturbations. Our phrase-level attack has a success rate of 89.75% against XLM-R large , bringing its average accuracy of 79.85 down to 8.18 on XNLI. Finally, we propose an efficient adversarial training scheme that trains in the same number of steps as the original model and show that it improves model accuracy. 1 Original P: The girl that can help me is all the way across town. H: There is no one who can help me. Adversary P: olan girl that can help me is all the way across town. H: one who can help me. Prediction Before: Contradiction After: Entailment Original P: We didn't know where they were going. H: We didn't know where the people were traveling to. Adversary P: We didn't know where they were going. H: We didn't know where les gens allaient. Prediction Before: Entailment After: Neutral Original P: Well it got to where there's two or three aircraft arrive in a week and I didn't know where they're flying to.H: There are never any aircraft arriving. Adversary P: общем, дошло до mahali there's two or three aircraft arrive in a week and I didn't know where they're flying to.