With the rise of mass customization, manufacturing companies are increasingly adopting mixed-model assembly lines. These lines can produce multiple products instead of a single one in a dedicated manufacturing system. Consequently, mixed-model assembly lines can benefit from reconfigurations of the workforce and equipment to adjust the line to the production requirements. This study investigates the impact of dynamic task assignment on the design of a mixed-model assembly line with walking workers. In the dynamic task assignment strategy, the assignment of tasks to stations changes depending on the item sequence. In this work, we propose a scenario-based integer linear program to design such an assembly line. The numerical results show that the dynamic task assignment strategy significantly reduces the number of required workers when compared to the fixed task assignment strategy, but it slightly increases the total equipment costs.