diff --git a/doit/cmd_forget.py b/doit/cmd_forget.py
index 92b8762b..5bde3eb6 100644
--- a/doit/cmd_forget.py
+++ b/doit/cmd_forget.py
@@ -52,6 +52,8 @@ def _execute(self, forget_sub, forget_disable_default, forget_all):
         # forget tasks from list
         else:
             tasks = dict([(t.name, t) for t in self.task_list])
+            if self.sel_tasks is None:
+                self.sel_tasks = list(tasks.keys())
             check_tasks_exist(tasks, self.sel_tasks)
             forget_list = self.sel_tasks