diff --git a/work.py b/work.py
index d71cc4b2b9..15420151e3 100644
--- a/work.py
+++ b/work.py
@@ -484,7 +484,7 @@ class Work:
 
             if constraint_finish:
                 late_finish = self.add_hours(work.company, constraint_finish,
-                        -work.back_leveling_delay)
+                        -(work.back_leveling_delay or 0.0))
             else:
                 late_finish = None