diff --git a/magisch_corvee_script.py b/magisch_corvee_script.py
index 22fe847..2ebd2eb 100755
--- a/magisch_corvee_script.py
+++ b/magisch_corvee_script.py
@@ -77,7 +77,7 @@ def make_task_lut(tasks: dict[str, TaskConfig]):
             task_lut[lookup] |= {t.lower()}
     task_re = re.compile(config['task_re'])
     def lookup_tasks(tasks):
-        return set.union(*(task_lut[x.strip()] for x in task_re.split(tasks) if x not in config['ignore']))
+        return set.union(set(), *(task_lut[x.strip()] for x in task_re.split(tasks) if x not in config['ignore']))
     return lookup_tasks
 def read_prefs(pref_file, tasks, people):
     lookup_tasks = make_task_lut(tasks)