When naming pictures in mixed-language blocks, bilinguals sometimes exhibit reversed language dominance effects. These have been attributed to proactive inhibitory control of the dominant language, or adaptation of language-specific selection thresholds. Even though reversed dominance arguably provides the most striking evidence of inhibition, few studies have focused on when and why this effect occurs. We investigated this topic in a large data set (>400 bilinguals) using a continuous and objective measure of language dominance. We found larger reversed language dominance effects in more (vs. less) balanced bilinguals in mixed-language blocks. However, after taking into account standard language dominance effects in single-language blocks, the extent to which dominance effects changed across block types was actually significantly smaller for more balanced bilinguals, which is in line with the inhibitory control account. Interestingly, dominance reversal was not associated with increased overall speed in the mixed-language block. Thus, dominance reversal is more likely in balanced bilinguals not because they are better at applying proactive control, but because they are more likely to overshoot when the goal is to make both languages about equally accessible – and overall, unbalanced bilinguals apply more proactive control than balanced bilinguals to facilitate picture naming in mixed-language blocks.