We investigate how to counter misinformation about voter and election fraud using data from the US and Brazil. Our study first compares two types of messages countering claims of widespread fraud: (i) retrospective corrections from credible sources speaking against interest and (ii) prebunking messages that prospectively warn of false claims about future elections and provide information about election security practices. In the US, each approach immediately increased election confidence and reduced fraud beliefs, with prebunking showing somewhat more durable effects. In Brazil, prebunking had positive immediate effects across measured outcomes, whereas those of the credible source corrections were less consistent. We then conducted an experiment in the US randomizing exposure to a persuasion forewarning before election security information is provided. Prebunking again increased confidence and decreased fraud beliefs but only when the forewarning was omitted, suggesting that novel factual information is responsible for the observed effects of the prebunking treatment.