diff --git a/packages/service-core/src/storage/mongo/MongoWriteCheckpointAPI.ts b/packages/service-core/src/storage/mongo/MongoWriteCheckpointAPI.ts
index bbcebb0de..966eb77be 100644
--- a/packages/service-core/src/storage/mongo/MongoWriteCheckpointAPI.ts
+++ b/packages/service-core/src/storage/mongo/MongoWriteCheckpointAPI.ts
@@ -111,9 +111,16 @@ export class MongoWriteCheckpointAPI implements WriteCheckpointAPI {
   }
 
   protected async lastManagedWriteCheckpoint(filters: ManagedWriteCheckpointFilters) {
-    const { user_id } = filters;
+    const { user_id, heads } = filters;
+    // TODO: support multiple heads when we need to support multiple connections
+    const lsn = heads['1'];
+    if (lsn == null) {
+      // Can happen if we haven't replicated anything yet.
+      return null;
+    }
     const lastWriteCheckpoint = await this.db.write_checkpoints.findOne({
-      user_id: user_id
+      user_id: user_id,
+      'lsns.1': { $lte: lsn }
     });
     return lastWriteCheckpoint?.client_id ?? null;
   }
diff --git a/packages/service-core/test/src/sync.test.ts b/packages/service-core/test/src/sync.test.ts
index 64e463274..75e5f550f 100644
--- a/packages/service-core/test/src/sync.test.ts
+++ b/packages/service-core/test/src/sync.test.ts
@@ -1,6 +1,6 @@
 import { SaveOperationTag } from '@/storage/storage-index.js';
 import { RequestTracker } from '@/sync/RequestTracker.js';
-import { streamResponse } from '@/sync/sync.js';
+import { streamResponse, SyncStreamParameters } from '@/sync/sync.js';
 import { StreamingSyncLine } from '@/util/protocol-types.js';
 import { JSONBig } from '@powersync/service-jsonbig';
 import { RequestParameters } from '@powersync/service-sync-rules';
@@ -381,6 +381,67 @@ function defineTests(factory: StorageFactory) {
       })
     });
   });
+
+  test('write checkpoint', async () => {
+    const f = await factory();
+
+    const syncRules = await f.updateSyncRules({
+      content: BASIC_SYNC_RULES
+    });
+
+    const storage = f.getInstance(syncRules);
+    await storage.autoActivate();
+
+    await storage.startBatch(BATCH_OPTIONS, async (batch) => {
+      // <= the managed write checkpoint LSN below
+      await batch.commit('0/1');
+    });
+
+    const checkpoint = await storage.createManagedWriteCheckpoint({
+      user_id: 'test',
+      heads: { '1': '1/0' }
+    });
+
+    const params: SyncStreamParameters = {
+      storage: f,
+      params: {
+        buckets: [],
+        include_checksum: true,
+        raw_data: true
+      },
+      parseOptions: PARSE_OPTIONS,
+      tracker,
+      syncParams: new RequestParameters({ sub: 'test' }, {}),
+      token: { sub: 'test', exp: Date.now() / 1000 + 10 } as any
+    };
+    const stream1 = streamResponse(params);
+    const lines1 = await consumeCheckpointLines(stream1);
+
+    // If write checkpoints are not correctly filtered, this may already
+    // contain the write checkpoint.
+    expect(lines1[0]).toMatchObject({
+      checkpoint: expect.objectContaining({
+        last_op_id: '0',
+        write_checkpoint: undefined
+      })
+    });
+
+    await storage.startBatch(BATCH_OPTIONS, async (batch) => {
+      // must be >= the managed write checkpoint LSN
+      await batch.commit('1/0');
+    });
+
+    // At this point the LSN has advanced, so the write checkpoint should be
+    // included in the next checkpoint message.
+    const stream2 = streamResponse(params);
+    const lines2 = await consumeCheckpointLines(stream2);
+    expect(lines2[0]).toMatchObject({
+      checkpoint: expect.objectContaining({
+        last_op_id: '0',
+        write_checkpoint: `${checkpoint}`
+      })
+    });
+  });
 }
 
 /**