diff --git a/services/web/app/src/models/Project.mjs b/services/web/app/src/models/Project.mjs
index e7a4b3968f..aa767f2f1b 100644
--- a/services/web/app/src/models/Project.mjs
+++ b/services/web/app/src/models/Project.mjs
@@ -88,6 +88,7 @@ export const ProjectSchema = new Schema(
         rangesSupportEnabled: { type: Boolean },
         otMigrationStage: { type: Number },
       },
+      isDebugCopyOf: { type: ObjectId },
     },
     collabratecUsers: [
       {
diff --git a/tools/migrations/20260114135706_create-debug-project-indexes.mjs b/tools/migrations/20260114135706_create-debug-project-indexes.mjs
new file mode 100644
index 0000000000..d9997ffe01
--- /dev/null
+++ b/tools/migrations/20260114135706_create-debug-project-indexes.mjs
@@ -0,0 +1,31 @@
+/* eslint-disable no-unused-vars */
+
+import Helpers from './lib/helpers.mjs'
+
+const tags = ['saas']
+
+const indexes = [
+  {
+    key: { 'overleaf.isDebugCopyOf': 1, owner_ref: 1, lastUpdated: 1 },
+    name: 'owner_ref_1_lastUpdated_1_debugCopies',
+    partialFilterExpression: {
+      'overleaf.isDebugCopyOf': { $type: 'objectId' },
+    },
+  },
+]
+
+const migrate = async client => {
+  const { db } = client
+  await Helpers.addIndexesToCollection(db.projects, indexes)
+}
+
+const rollback = async client => {
+  const { db } = client
+  await Helpers.dropIndexesFromCollection(db.projects, indexes)
+}
+
+export default {
+  tags,
+  migrate,
+  rollback,
+}