diff --git a/src/blenderbim/blenderbim/tool/sequence.py b/src/blenderbim/blenderbim/tool/sequence.py
index 2c6b8cb929..b0d12c6c07 100644
--- a/src/blenderbim/blenderbim/tool/sequence.py
+++ b/src/blenderbim/blenderbim/tool/sequence.py
@@ -207,10 +207,10 @@ class Sequence(blenderbim.core.tool.Sequence):
             if task.HasAssignments:
                 for rel in task.HasAssignments:
                     if rel.is_a("IfcRelAssignsToControl") and rel.RelatingControl.is_a("IfcWorkCalendar"):
-                        item.calendar = calendar.Name if calendar else ""
+                        item.calendar = calendar.Name or "Unnamed" if calendar else ""
             else:
                 item.calendar = ""
-                item.derived_calendar = calendar.Name if calendar else ""
+                item.derived_calendar = calendar.Name or "Unnamed" if calendar else ""
 
             if task.TaskTime:
                 task_time = task.TaskTime