Opportunistic reuse is a need based sourcing of software modules without a prior reuse plan. It is a common tactical approach in software development. Developers often reuse an external software module opportunistically to improve their productivity. But, studies have shown that this results in extensive refactoring and adds maintenance owes. We assert this problem to the mismatches between the software under development and the reused external module; caused because of their different assumptions and constraints. We highlight the problems of such opportunistic reuse practices with the help of a case study. In our study, we found issues such as unanticipated behavior, violated constraints, conflict in assumption, fragile structure, and software bloat. In this paper, we like to draw attention of the research community to the wide spread opportunistic reuse practices and the lack of methods to pro‐actively identify and resolve the mismatches. We propose the need for supporting developers in reasoning before reuse from the perspective of identifying and fixing both local and global mismatches. Furthermore, we identify other opportunistic software development practices where similar issues can be observed and also suggest the research areas where further investigation can benefit developers in improving their productivity. Copyright © 2016 John Wiley & Sons, Ltd.