diff --git a/docs/adr/040-timeline-domain-data-model.md b/docs/adr/040-timeline-domain-data-model.md
index 5ae61f17..30f5767a 100644
--- a/docs/adr/040-timeline-domain-data-model.md
+++ b/docs/adr/040-timeline-domain-data-model.md
@@ -109,4 +109,7 @@ the event intact (V71/ADR-032 hardening — a person delete must never 500).
 - The `timeline → document.DatePrecision` compile coupling is permanent until a shared-package
   refactor; precedent already exists (`importing/DocumentImporter`, `person`).
 - The service/controller/DTO layer (#775) inherits the view-assembly, optimistic-lock
-  translation, forgery-guard, and permission obligations recorded above.
+  translation, forgery-guard, and permission obligations recorded above. It must also add a
+  service-level title-length check (new `ErrorCode`, e.g. `TIMELINE_TITLE_TOO_LONG`, mirroring
+  `GESCHICHTE_TITLE_TOO_LONG`) — `title` is `VARCHAR(255)`, and without the guard an over-long
+  title surfaces as a raw `DataIntegrityViolationException` → HTTP 500.