EventSource · rexxars · Aug 20, 2026 · Aug 20, 2026
diff --git a/.changeset/lasteventid-persists-without-id.md b/.changeset/lasteventid-persists-without-id.md
diff --git a/.changeset/persist-ids-from-data-less-blocks.md b/.changeset/persist-ids-from-data-less-blocks.md
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # 📓 Changelog
 
+## 5.1.1
+
+### Patch Changes
+
+- [#358](https://github.com/EventSource/eventsource/pull/358) [`de3c0ae`](https://github.com/EventSource/eventsource/commit/de3c0ae75bfffea4f5862950c386b3ddd6e3e64c) Thanks [@pacocartones](https://github.com/pacocartones)! - Fixed `MessageEvent.lastEventId` being empty when a message omits the id field
+
+  The `lastEventId` attribute is the last event ID string of the event source, so an explicit `id` field persists until another one replaces it. Message events were dispatched with the current event's own `id` instead of that buffer, which left `lastEventId` empty on every event that omitted `id`, even though the buffer still held the earlier value and would have been sent as `Last-Event-ID` on reconnect.
+
+- [`17a9772`](https://github.com/EventSource/eventsource/commit/17a97722ed3f06920e931b627b9ef86752be165f) Thanks [@rexxars](https://github.com/rexxars)! - Fixed ID-only event blocks not updating `MessageEvent.lastEventId` or `Last-Event-ID` on reconnect.
+
 ## 5.1.0
 
 ### Minor Changes

diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "eventsource",
-  "version": "5.1.0",
+  "version": "5.1.1",
   "description": "WhatWG/W3C compliant EventSource client for Node.js and browsers",
   "keywords": [
     "eventsource",