diff --git a/packages/core/src/baseclient.ts b/packages/core/src/baseclient.ts
index 260eb412561b..1c8de1472a49 100644
--- a/packages/core/src/baseclient.ts
+++ b/packages/core/src/baseclient.ts
@@ -287,10 +287,13 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
    */
   public sendEvent(event: Event, hint: EventHint = {}): void {
     if (this._dsn) {
-      const env = createEventEnvelope(event, this._dsn, this._options._metadata, this._options.tunnel);
+      let env = createEventEnvelope(event, this._dsn, this._options._metadata, this._options.tunnel);
 
       for (const attachment of hint.attachments || []) {
-        addItemToEnvelope(env, createAttachmentEnvelopeItem(attachment, this._options.transportOptions?.textEncoder));
+        env = addItemToEnvelope(
+          env,
+          createAttachmentEnvelopeItem(attachment, this._options.transportOptions?.textEncoder),
+        );
       }
 
       this._sendEnvelope(env);
diff --git a/packages/core/test/lib/attachments.test.ts b/packages/core/test/lib/attachments.test.ts
new file mode 100644
index 000000000000..610518225793
--- /dev/null
+++ b/packages/core/test/lib/attachments.test.ts
@@ -0,0 +1,38 @@
+import { parseEnvelope } from '@sentry/utils/test/testutils';
+import { TextEncoder } from 'util';
+
+import { createTransport } from '../../src/transports/base';
+import { getDefaultTestClientOptions, TestClient } from '../mocks/client';
+
+describe('Attachments', () => {
+  beforeEach(() => {
+    TestClient.sendEventCalled = undefined;
+    TestClient.instance = undefined;
+  });
+
+  afterEach(() => {
+    jest.clearAllMocks();
+  });
+
+  test('actually end up in envelope', async () => {
+    expect.assertions(4);
+
+    const options = getDefaultTestClientOptions({
+      dsn: 'https://username@domain/123',
+      enableSend: true,
+      transport: () =>
+        createTransport({ recordDroppedEvent: () => undefined, textEncoder: new TextEncoder() }, async req => {
+          const [, items] = parseEnvelope(req.body);
+          expect(items.length).toEqual(2);
+          // Second envelope item should be the attachment
+          expect(items[1][0]).toEqual({ type: 'attachment', length: 50000, filename: 'empty.bin' });
+          expect(items[1][1]).toBeInstanceOf(Uint8Array);
+          expect((items[1][1] as Uint8Array).length).toEqual(50_000);
+          return {};
+        }),
+    });
+
+    const client = new TestClient(options);
+    client.captureEvent({}, { attachments: [{ filename: 'empty.bin', data: new Uint8Array(50_000) }] });
+  });
+});