diff --git a/lib/tasks/migrate_from_trac.rake b/lib/tasks/migrate_from_trac.rake
index 7fe1f09ac..48a774eef 100644
--- a/lib/tasks/migrate_from_trac.rake
+++ b/lib/tasks/migrate_from_trac.rake
@@ -92,7 +92,7 @@ namespace :redmine do
         set_table_name :milestone
         
         def due
-          if read_attribute(:due) > 0
+          if read_attribute(:due) && read_attribute(:due) > 0
             Time.at(read_attribute(:due)).to_date
           else
             nil