diff --git a/app/tasks/maintenance/backfill_invalid_dossiers_for_tiers_task.rb b/app/tasks/maintenance/backfill_invalid_dossiers_for_tiers_task.rb
new file mode 100644
index 000000000..ac99289eb
--- /dev/null
+++ b/app/tasks/maintenance/backfill_invalid_dossiers_for_tiers_task.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Maintenance
+  class BackfillInvalidDossiersForTiersTask < MaintenanceTasks::Task
+    def collection
+      Dossier.where(for_tiers: true).where(mandataire_first_name: nil)
+    end
+
+    def process(element)
+      element.update_column(for_tiers: false)
+    end
+  end
+end