diff --git a/src/device-sync/__tests__/app/lifecycle.test.ts b/src/device-sync/__tests__/app/lifecycle.test.ts
index b95b0bb1..18729359 100644
--- a/src/device-sync/__tests__/app/lifecycle.test.ts
+++ b/src/device-sync/__tests__/app/lifecycle.test.ts
@@ -43,7 +43,8 @@ vi.mock('../../native', () => ({
   ensureAndroidAccount: vi.fn(async (name: string, registryId: string) => {
     h.state.log.push(`ensure ${name}`);
     const existing = h.find(name);
-    if (existing && existing.registryId !== registryId) throw new Error('conflict');
+    // As the native module rejects (DeviceSyncAccounts.ensure → AccountConflictException).
+    if (existing && existing.registryId !== registryId) throw Object.assign(new Error(`${name} belongs to another app account`), { code: 'conflict' });
     if (existing) return false;
     h.state.accounts.push({ name, registryId, sync: {} });
     return true;
@@ -212,6 +213,18 @@ describe('enable', () => {
     expect(outcome).toEqual({ kind: 'enabled', accountName: ALICE });
   });
 
+  it('adds no second account named after the registry id when adding the account fails for another reason', async () => {
+    for (const code of ['failed', 'permission']) {
+      vi.mocked(native.ensureAndroidAccount).mockClear();
+      vi.mocked(native.ensureAndroidAccount).mockRejectedValueOnce(Object.assign(new Error(`AccountManager said no (${code})`), { code }));
+      const outcome = await enableDeviceSync(ALICE, CONTACTS_AUTHORITY);
+      expect(outcome).toEqual({ kind: 'failed', message: `AccountManager said no (${code})` });
+      expect(native.ensureAndroidAccount).toHaveBeenCalledTimes(1);
+      expect(h.state.accounts).toEqual([]);
+      expect(accountDeviceSync(ALICE).androidAccountName).toBeUndefined();
+    }
+  });
+
   it('leaves no account behind when turning sync on fails', async () => {
     h.state.failSetSyncEnabled = true;
     const outcome = await enableDeviceSync(ALICE, CONTACTS_AUTHORITY);
diff --git a/src/device-sync/app/lifecycle.ts b/src/device-sync/app/lifecycle.ts
index 4daba392..6f058c71 100644
--- a/src/device-sync/app/lifecycle.ts
+++ b/src/device-sync/app/lifecycle.ts
@@ -122,8 +122,9 @@ async function ensureAccountFor(registryId: string): Promise<string> {
     await ensureAndroidAccount(name, registryId);
     return name;
   } catch (err) {
-    // The name belongs to another app account after all (the list was stale).
-    if (name === registryId) throw err;
+    // The name belongs to another app account after all (the list was stale). Any
+    // other failure fails the turn-on: a second account would show in the apps.
+    if (name === registryId || (err as { code?: unknown } | null)?.code !== 'conflict') throw err;
     await ensureAndroidAccount(registryId, registryId);
     return registryId;
   }