diff --git a/backend/__tests__/unit/models/AgentMemory.test.ts b/backend/__tests__/unit/models/AgentMemory.test.ts
index 6c2fcfff19..90eb235fd4 100644
--- a/backend/__tests__/unit/models/AgentMemory.test.ts
+++ b/backend/__tests__/unit/models/AgentMemory.test.ts
@@ -9,6 +9,7 @@ const { setupMongoDb, closeMongoDb, clearMongoDb } = require('../../utils/testUt
 describe('AgentMemory (ADR-003 v2 schema)', () => {
   beforeAll(async () => {
     await setupMongoDb();
+    await AgentMemory.syncIndexes();
   });
 
   afterAll(async () => {
diff --git a/backend/__tests__/unit/models/User.test.js b/backend/__tests__/unit/models/User.test.js
index a6374980ee..0db026d18c 100644
--- a/backend/__tests__/unit/models/User.test.js
+++ b/backend/__tests__/unit/models/User.test.js
@@ -11,6 +11,11 @@ describe('User Model Tests', () => {
   // Setup and teardown for MongoDB
   beforeAll(async () => {
     await setupMongoDb();
+    // These duplicate-write assertions require the indexes to exist first.
+    // Use explicit indexes: User.syncIndexes() conflicts with the model's
+    // separate collation index on username.
+    await User.collection.createIndex({ username: 1 }, { unique: true });
+    await User.collection.createIndex({ email: 1 }, { unique: true });
   });
 
   afterAll(async () => {