The term “design fixation” refers to a phenomenon where designers unknowingly limit the space within which they search for solutions. In an attempt to study this phenomenon experimentally, researchers typically set participants open-ended design problems, prime them with an example solution, and measure their performance through a variety of subjective metrics. This approach gives rise to various problems, including limited data capture and highly subjective evaluation of design behavior. To address these problems, we studied design fixation with a computer-based task inspired by psychological paradigms used to study “mental set” (also known as the “Einstellung effect”). The task consisted of a gamelike activity requiring participants to design a bridge within a specified budget. The use of a digital environment facilitated continuous data capture during the design activities. The constrained task (and direct quantitative measures) permitted a more objective analysis of design performance, including the occurrence of fixation. The results showed that participants who developed a mental set during the task failed to find alternative, more efficient solutions in trials admitting multiple solutions, compared to the participants who did not fall victim to this mental block. In addition, during the process of designing, the occurrence of mental set resulted in participants adopting a less efficient design behavior and reporting a different subjective experience of the task. The method used and the results obtained show an exciting alternative for studying design fixation experimentally and promote a wider exploration of the variety of design activities in which fixation might occur.