diff --git a/package-lock.json b/package-lock.json
index af7455c81..aa74ab842 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "munder-difflin",
-  "version": "0.4.6",
+  "version": "0.5.5-sixth.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "munder-difflin",
-      "version": "0.4.6",
+      "version": "0.5.5-sixth.1",
       "hasInstallScript": true,
       "dependencies": {
         "@codemirror/lang-css": "^6.3.1",
diff --git a/package.json b/package.json
index eb5a2384d..cf27a157e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "munder-difflin",
-  "version": "0.4.6",
+  "version": "0.5.5-sixth.1",
   "private": true,
   "description": "Clones for you and your team, working 24/7 — a free, local-first multi-agent harness that turns the CLI coding agent you already run into a clone of you, coordinating an office of agents on your machine.",
   "main": "out/main/index.js",
diff --git a/test/fork-version.test.cjs b/test/fork-version.test.cjs
new file mode 100644
index 000000000..3215f7116
--- /dev/null
+++ b/test/fork-version.test.cjs
@@ -0,0 +1,34 @@
+'use strict';
+// This fork carries upstream's public 0.5.5 plus its own changes, labelled
+// 0.5.5-sixth.N. The updater compares major.minor.patch only, so the label must
+// read as 0.5.5 there: upstream's 0.5.5 release is not offered as an update
+// over it, and anything upstream ships after it still is.
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+const loadTs = require('./load-ts.cjs');
+
+const { isNewer, parseVersion, shouldShowReleaseDrop } = loadTs('src/shared/updateState.ts');
+const { version } = require(path.resolve(__dirname, '..', 'package.json'));
+
+test('the fork labels itself as a build of 0.5.5', () => {
+  assert.match(version, /^0\.5\.5-sixth\.\d+$/);
+  assert.deepEqual(parseVersion(version), [0, 5, 5]);
+});
+
+test('upstream\'s 0.5.5 release is not offered as an update over the fork', () => {
+  // The releases/latest notifier offers a tag when isNewer(tag, running).
+  assert.equal(isNewer('v0.5.5', version), false);
+  assert.equal(isNewer('v0.5.3', version), false);
+});
+
+test('a later upstream release is still offered', () => {
+  assert.equal(isNewer('v0.5.6', version), true);
+  assert.equal(isNewer('v0.6.0', version), true);
+});
+
+test('moving from 0.4.6 to the fork label opens the release notes once', () => {
+  assert.equal(shouldShowReleaseDrop('0.4.6', version), true);
+  assert.equal(shouldShowReleaseDrop(version, version), false);
+});