The ego-depletion effect refers to a temporary failure of self-control exertion after first performing an effortful task. This phenomenon has experienced a replication crisis in the past few years. In the present series of experiments, we tried to replicate the ego-depletion effect using a 30-min modified Stroop task tapping two executive functions (inhibitory control and cognitive flexibility) as the depleting task. In the first study, we compared the performance of a handgrip endurance task after this depleting task or after a classic control task (i.e., reading color words) and failed to replicate the ego-depletion effect. We showed that the control task induced boredom and subjective fatigue. In a second study, we looked for a better control task and compared the color-word reading task to another possible control task used in the literature (i.e., watching a documentary). Controlling for boredom, subjective fatigue, motivation and affective state, we found that the video task was not boring and did not induce fatigue, drop in motivation or negative affective state, whereas the color-word reading task did. In a third study, we used the video task as the control task and the modified effortful Stroop task used in the first study as the depleting task and succeeded in replicating the ego-depletion effect. This series of experiments illustrates that the choice of an appropriate control task is crucial to observe an ego-depletion effect and that boredom is costly. Consequently, it appears necessary to control for boredom in any future replication study aiming to observe an ego-depletion effect.