A bank should provide reliable financial services to its customers. Banking services are evolving along with information technology advancement. It is a common practice for every organization to adopt the latest technology to gain or sustain their competitive advantage against competitors. Nevertheless, not every technology implemented in banks is a state of the art technology. They come from a different extent, and these older generation technologies are called the legacy system. The mainframe is usually a part of a legacy system because it exists since the organization was established. The mainframe managed a humongous financial transaction at a time. Its reliable performance makes it indispensable. Therefore, banks are facing the interoperability challenges between the legacy system and new technologies. This study will analyze the approach used by a bank in Indonesia in embracing agile development principles in implementing new technologies above their rigid legacy infrastructure.