In ten member states of the European Union (EU) the new constitutional treaty was supposed to be ratified by referendum. A growing number of theoretical models predicts that such additional ratification hurdles result in an advantage for negotiators in the bargaining game. The impact such a referendum constraint can exert, however, depends on the timing of its announcement, the remaining ratification rules as well as the preference constellations. If parliament and voters are actually in favor of the new treaty, ratification constraints may cease to affect the bargaining outcome. After presenting the theoretical foundation of these arguments, we present empirical evidence much in line with the theoretical implications. More specifically, especially for the issues changed during the intergovernmental conference, those governments gained that had scheduled a referendum and voters had a stronger preference for the status quo.