Custom-developed adaptations of software products are increasingly important to meet different and changing customer needs and heterogeneous system environments. Efficient software customization processes with short lead times are thus a priority for companies to stay competitive. The purpose of this case study is to identify waste-related problems in a software product customization process by using value stream maps (VSM). The study was conducted at the telecom company Ericsson AB; the empirical data was collected using document analysis, extraction of phase times from a requirements tracking tool and interviews. It was used to construct a value stream map that showed the present state of the process. The map was then used in interviews with key stakeholders where they identified waste and proposed measures to avoid them. These solution proposals were subsequently used to construct a future value stream map showing a reduced lead time. Static validation showed that the VSM methodology was useful and that the identified solutions were of value. Our results have applicability for software engineering process improvement in general and for customization processes in particular.