diff --git a/services/web/migrations/20250828100935_drop_old_lastBackedUpVersion_index.mjs b/services/web/migrations/20250828100935_drop_old_lastBackedUpVersion_index.mjs
new file mode 100644
index 0000000000..45662cc037
--- /dev/null
+++ b/services/web/migrations/20250828100935_drop_old_lastBackedUpVersion_index.mjs
@@ -0,0 +1,36 @@
+/* eslint-disable no-unused-vars */
+
+import Helpers from './lib/helpers.mjs'
+
+const tags = ['saas']
+
+const indexes = [
+  {
+    key: { 'overleaf.backup.lastBackedUpVersion': 1 },
+    name: 'overleaf.backup.lastBackedUpVersion_1',
+    partialFilterExpression: {
+      'overleaf.backup.lastBackedUpVersion': { $in: [null] },
+    },
+  },
+]
+
+const migrate = async client => {
+  const { db } = client
+  // Ensure the optimisation migration has run first to create the new index
+  await Helpers.assertDependency(
+    '20250827155732_optimise_lastBackedUpVersion_index'
+  )
+  // Drop the old index from 20250307120446_create_project_lastBackedUpVersion_index
+  await Helpers.dropIndexesFromCollection(db.projects, indexes)
+}
+
+const rollback = async client => {
+  const { db } = client
+  await Helpers.addIndexesToCollection(db.projects, indexes)
+}
+
+export default {
+  tags,
+  migrate,
+  rollback,
+}