Before 12 January 1377, Friedrich XI married Adelheid (d. 1413), a daughter of Count Hugo of Fürstenberg-Zindelstein. Her brother Johann was the last Count of Fürstenberg-Haslah. Johann died childless in the Battle of Sempach of 1386, and Friedrich XI inherited Bräunlingen from him, which gave rise to a lengthy dispute with the main line of the Fürstenberg family.