This article reconstructs the history of Kling Muslims’ contribution to the religious and ethnic cosmopolitanism of sixteenth-century Ayutthaya. This study's argument is constructed based on an aggregate of written fragments about the Kling in both Portuguese primary sources and the wider academic literature. We reveal that, amongst the many ways in which Siam benefited from the Iberian invasion of Melaka in 1511, the dramatic geopolitical rupture of the invasion re-routed trade across the Bay of Bengal. As a result, Kling merchants began arriving in Ayutthaya in greater numbers via the new network of Siamese-controlled ports and portages. Moreover, this study demonstrates the utility of greater synergy among South Asian, Southeast Asian, Thai, and Malay Studies through focusing on the exonyms employed in primary and secondary sources. Finally, this article contends that Ayutthaya's ethnic and religious cosmopolitanism was impacted by the arrival of South Asian Muslims, referred to as Kling in the Malay World and Khaek in Siam, approximately one century before Persians arrived in greater numbers. This, among others, was an unintended result of Portugal's sixteenth-century interventions into, and alliances with, the Siamese.