This paper illustrates the effects of post-merger integration speed on M&A performance and the moderating role of decision-making preferences. For a better understanding of the effects of integration speed, we separate the role of human and task integration speed. The results, obtained from a survey based on 99 M&A transactions with acquirers from the German speaking part of Europe, indicate that fast human integration is beneficial to M&A performance while fast task integration has a significant negative effect. Furthermore our results suggest that the effects of human and task integration speed are moderated by the decision-making style of those in charge of the transactions and of integration. Different from what we expected, our results indicate that a preference for intuitive decision-making moderates the relation between task integration speed and M&A performance significant and positive, while a preference for deliberate decision-making moderates the relation between human integration speed and M&A performance.