diff --git a/inginious/frontend/pages/course_admin/task_list.py b/inginious/frontend/pages/course_admin/task_list.py
index 983d6294c..b33939f27 100644
--- a/inginious/frontend/pages/course_admin/task_list.py
+++ b/inginious/frontend/pages/course_admin/task_list.py
@@ -38,7 +38,8 @@ def POST_AUTH(self, courseid):  # pylint: disable=arguments-differ
             task_dispenser = course.get_task_dispenser()
             try:
                 data = task_dispenser.import_legacy_tasks()
-                for taskid, task in data["config"].items():
+                dispenser_data = task_dispenser.get_dispenser_data()
+                for task in dispenser_data["config"].values():
                     task["accessibility"] = dict_data_str_to_datetimes(
                             change_access_structure(task["accessibility"], True))
                 self.update_dispenser(course, data)
diff --git a/inginious/frontend/pages/taskset_admin/template.py b/inginious/frontend/pages/taskset_admin/template.py
index 6805e7a6f..267c7c841 100644
--- a/inginious/frontend/pages/taskset_admin/template.py
+++ b/inginious/frontend/pages/taskset_admin/template.py
@@ -39,7 +39,8 @@ def POST_AUTH(self, tasksetid):  # pylint: disable=arguments-differ
             task_dispenser = taskset.get_task_dispenser()
             try:
                 data = task_dispenser.import_legacy_tasks()
-                for taskid, task in data["config"].items():
+                dispenser_data = task_dispenser.get_dispenser_data()
+                for task in dispenser_data["config"].values():
                     task["accessibility"] = dict_data_str_to_datetimes(
                         change_access_structure(task["accessibility"], True))
                 self.update_dispenser(taskset, data)
diff --git a/inginious/frontend/task_dispensers/toc.py b/inginious/frontend/task_dispensers/toc.py
index e72859b83..197983b9a 100644
--- a/inginious/frontend/task_dispensers/toc.py
+++ b/inginious/frontend/task_dispensers/toc.py
@@ -13,7 +13,7 @@
     SubmissionLimit, Accessibility
 from inginious.frontend.task_dispensers import TaskDispenser
 from inginious.frontend.accessible_time import AccessibleTime
-from inginious.frontend.util import change_access_structure, dict_data_str_to_datetimes, dict_data_datetimes_to_str
+from inginious.frontend.util import dict_data_datetimes_to_str
 
 
 class TableOfContents(TaskDispenser):
@@ -144,7 +144,14 @@ def get_ordered_tasks(self):
         return OrderedDict([(taskid, tasks[taskid]) for taskid in self._toc.get_tasks() if taskid in tasks])
 
     def has_legacy_tasks(self, ignore_imported=False):
-        """ Checks if the task files contains dispenser settings """
+        """ Checks if the task files contains dispenser settings or if the tasks have legacy structure """
+
+        if "config" in self._dispenser_data:
+            # if old accessibility structure
+            for task in self._dispenser_data["config"].values():
+                if isinstance(task["accessibility"], str):
+                    return True
+
         if not ignore_imported and self._dispenser_data.get("imported", False):
             return False