When people engage in joint activities together, they use dialogue, and more specifically project markers such as yeah, okay, or uh-huh, to coordinate entrances and exits of projects and subprojects. The purpose of the current study was to examine how two features of the dialogue situation, namely, mental load and face visibility, affect project marker production. Pairs of participants performed a collaborative puzzle game together. Mental load was manipulated through time pressure; visibility was manipulated by allowing the participants to see each other’s face during the task, or not. Dialogues were transcribed and coded for project marker production. Project marker production was found to increase under mental load; this also depended on the role of the speaker in the dyad (Director or Matcher) and on face visibility. This sheds light on the idea that dialogue partners may behave more collaboratively when experiencing high levels of mental load, contributing to a better understanding of mental resource allocation in dialogue-based joint activities.