The present studies tested the effectiveness of implementation intentions with an “if situation, then not habitual response” structure. Based on ironic process theory and the literature on the processing of negations, it was expected that these “negation implementation intentions” would, ironically, strengthen the habit (situation—response association) one aims to break. In line with the hypotheses, forming negation implementation intentions resulted in cognitive ironic rebound effects as well as behavioral ironic rebound effects compared to an intention only condition or a replacement implementation intention. Additionally, it was found that negation implementation intentions are most likely to result in ironic rebound effects when the habit to be negated is strong. Although implementation intentions are generally highly effective in facilitating behavior change even when this involves breaking unwanted habits, the present research suggests that they are ineffective when they have a negating structure.