Analysis of information sources in references of the Wikipedia article "Κανονισμοί του Διαγωνισμού Τραγουδιού Eurovision" in Greek language version.
The songs of the contest were not to exceed three and a half minutes
Swedish participant Ingvar Wixell performed his song -originally called Annorstädes Vals - in English instead of Swedish while all the other participants sang in their native languages. This incident led to a rule change meaning that all participants would have to perform their songs in their respective national languages.