diff --git a/static/js/offline-sync.js b/static/js/offline-sync.js
index e529131..056641c 100644
--- a/static/js/offline-sync.js
+++ b/static/js/offline-sync.js
@@ -7,6 +7,15 @@
 
 const BACKGROUND_SYNC_MIN_INTERVAL_MS = 2 * 60 * 1000;
 
+// Bump this whenever a previously-untracked entity type starts being synced
+// (e.g. tags/time_entries were added after tasks-only syncing already
+// shipped). /api/sync/ only returns rows changed since a device's last sync
+// token, so any device with an old token would otherwise never receive
+// pre-existing rows of the newly-tracked type - they were never "changed
+// since" a token issued before that type existed at all. Forces exactly one
+// full resync (by clearing the stored token) per bump, per device.
+const SYNC_FORMAT_VERSION = 2;
+
 function getCsrfToken() {
     const el = document.querySelector('[name=csrfmiddlewaretoken]');
     return el ? el.value : null;
@@ -103,7 +112,9 @@ async function runBackgroundSync() {
     }
 
     const deviceId = await ensureDeviceId();
-    const lastSyncToken = await getMeta('last_sync_token');
+    const syncFormatVersion = await getMeta('sync_format_version');
+    const forceFullResync = (syncFormatVersion || 1) < SYNC_FORMAT_VERSION;
+    const lastSyncToken = forceFullResync ? null : await getMeta('last_sync_token');
 
     const dirtyTasks = await getDirtyTasks();
     const dirtyTags = await getDirtyTags();
@@ -154,8 +165,12 @@ async function runBackgroundSync() {
 
     await setMeta('last_sync_token', data.sync_token);
     await setMeta('last_sync_at', new Date().toISOString());
+    await setMeta('sync_format_version', SYNC_FORMAT_VERSION);
 
-    return hadPendingChanges;
+    // A forced full resync just backfilled previously-missed data (e.g. tags
+    // that existed before tag syncing shipped) - worth a refresh even if
+    // nothing local was dirty, since the current page may be missing it too.
+    return hadPendingChanges || forceFullResync;
 }
 
 async function maybeBackgroundSync() {
diff --git a/templates/base.html b/templates/base.html
index 51117ba..ad6fdb9 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -148,7 +148,7 @@
     {% endblock %}
 
     <script src="{% static 'js/offline-db.js' %}?v=7"></script>
-    <script src="{% static 'js/offline-sync.js' %}?v=8"></script>
+    <script src="{% static 'js/offline-sync.js' %}?v=9"></script>
     <script src="{% static 'js/app.js' %}?v=8"></script>
     {% block extra_js %}{% endblock %}
 </body>