diff --git a/src/app/components/BackupRestore.test.tsx b/src/app/components/BackupRestore.test.tsx
index d2ccb2e628..311df7acaa 100644
--- a/src/app/components/BackupRestore.test.tsx
+++ b/src/app/components/BackupRestore.test.tsx
@@ -9,7 +9,10 @@ import { BackupRestoreTile } from './BackupRestore';
 const decodeRecoveryKey = vi.hoisted(() => vi.fn<(key: string) => Uint8Array>());
 const emitter = new TypedEventEmitter<string, Record<string, (...args: never[]) => void>>();
 const mockClient = Object.assign(emitter, {
-  secretStorage: { checkKey: vi.fn<() => Promise<boolean>>().mockResolvedValue(true) },
+  secretStorage: {
+    checkKey: vi.fn<() => Promise<boolean>>().mockResolvedValue(true),
+    get: vi.fn<(name: string) => Promise<string | undefined>>().mockResolvedValue('stored-key'),
+  },
   getSafeUserId: () => '@me:example.org',
   getDeviceId: () => 'DEVICE',
 });
diff --git a/src/app/components/BackupRestore.tsx b/src/app/components/BackupRestore.tsx
index 97643286da..0ac32a0123 100644
--- a/src/app/components/BackupRestore.tsx
+++ b/src/app/components/BackupRestore.tsx
@@ -46,6 +46,7 @@ import {
   menuIcon,
 } from '$components/icons/phosphor';
 import { InfoCard } from './info-card';
+import { restoreCrossSigningFromSecretStorage } from '$utils/matrix-crypto';
 
 type BackupKeyRecoveryProps = {
   crypto: CryptoApi;
@@ -70,7 +71,7 @@ function BackupKeyRecovery({
         storePrivateKey(secretStorageKeyId, recoveryKey);
 
         await cryptoBackend.processDeviceLists({ changed: [mx.getSafeUserId()] });
-        await cryptoBackend.bootstrapCrossSigning({});
+        await restoreCrossSigningFromSecretStorage(mx, cryptoBackend);
         await cryptoBackend.bootstrapSecretStorage({});
 
         // Emits KeyBackupDecryptionKeyCached, which drives the restore.
diff --git a/src/app/components/DeviceVerification.tsx b/src/app/components/DeviceVerification.tsx
index 34fdc796a0..ddf503971a 100644
--- a/src/app/components/DeviceVerification.tsx
+++ b/src/app/components/DeviceVerification.tsx
@@ -363,12 +363,23 @@ export function ReceiveSelfDeviceVerification() {
     const crypto = mx.getCrypto();
     if (!crypto?.getVerificationRequestsToDeviceInProgress) return undefined;
 
-    const pending = crypto
-      .getVerificationRequestsToDeviceInProgress(mx.getSafeUserId())
-      .find(
-        (candidate) => candidate.isSelfVerification && !candidate.initiatedByMe && candidate.pending
-      );
-    if (pending) setRequest(pending);
+    // The OlmMachine can be freed between the clientRunning check and this call.
+    try {
+      const pending = crypto
+        .getVerificationRequestsToDeviceInProgress(mx.getSafeUserId())
+        .find(
+          (candidate) =>
+            candidate.isSelfVerification && !candidate.initiatedByMe && candidate.pending
+        );
+      if (pending) setRequest(pending);
+    } catch (error) {
+      Sentry.addBreadcrumb({
+        category: 'crypto',
+        message: 'Could not read in-progress verification requests',
+        level: 'warning',
+        data: { error: error instanceof Error ? error.message : String(error) },
+      });
+    }
     return undefined;
   }, [mx]);
 
diff --git a/src/app/components/DeviceVerificationSetup.test.tsx b/src/app/components/DeviceVerificationSetup.test.tsx
new file mode 100644
index 0000000000..33bc422b9e
--- /dev/null
+++ b/src/app/components/DeviceVerificationSetup.test.tsx
@@ -0,0 +1,72 @@
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import type { CryptoApi } from '$types/matrix-sdk';
+import { DeviceVerificationSetup } from './DeviceVerificationSetup';
+
+const userHasCrossSigningKeys = vi.hoisted(() => vi.fn<() => Promise<boolean>>());
+const createRecoveryKeyFromPassphrase = vi.hoisted(() =>
+  vi.fn<CryptoApi['createRecoveryKeyFromPassphrase']>()
+);
+const bootstrapSecretStorage = vi.hoisted(() => vi.fn<() => Promise<void>>());
+const bootstrapCrossSigning = vi.hoisted(() => vi.fn<() => Promise<void>>());
+const resetKeyBackup = vi.hoisted(() => vi.fn<() => Promise<void>>());
+
+vi.mock('$hooks/useMatrixClient', () => ({
+  useMatrixClient: () => ({
+    getSafeUserId: () => '@me:example.org',
+    getCrypto: () =>
+      ({
+        userHasCrossSigningKeys,
+        createRecoveryKeyFromPassphrase,
+        bootstrapSecretStorage,
+        bootstrapCrossSigning,
+        resetKeyBackup,
+      }) as unknown as CryptoApi,
+  }),
+}));
+
+vi.mock('$client/secretStorageKeys', () => ({ clearSecretStorageKeys: vi.fn<() => void>() }));
+
+const submitSetup = () => {
+  const form = document.querySelector('form') as HTMLFormElement;
+  fireEvent.submit(form);
+};
+
+describe('DeviceVerificationSetup', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    createRecoveryKeyFromPassphrase.mockResolvedValue({
+      encodedPrivateKey: 'recovery-key',
+      privateKey: new Uint8Array([1, 2, 3]),
+    });
+    bootstrapSecretStorage.mockResolvedValue(undefined);
+    bootstrapCrossSigning.mockResolvedValue(undefined);
+    resetKeyBackup.mockResolvedValue(undefined);
+  });
+
+  it('refuses to set up again when the account already has cross-signing keys', async () => {
+    userHasCrossSigningKeys.mockResolvedValue(true);
+    render(<DeviceVerificationSetup onCancel={() => undefined} />);
+
+    submitSetup();
+
+    await waitFor(() =>
+      expect(screen.getByText(/already has device verification set up/)).toBeInTheDocument()
+    );
+    expect(createRecoveryKeyFromPassphrase).not.toHaveBeenCalled();
+    expect(bootstrapSecretStorage).not.toHaveBeenCalled();
+    expect(bootstrapCrossSigning).not.toHaveBeenCalled();
+    expect(resetKeyBackup).not.toHaveBeenCalled();
+  });
+
+  it('sets up when the account has no cross-signing keys', async () => {
+    userHasCrossSigningKeys.mockResolvedValue(false);
+    render(<DeviceVerificationSetup onCancel={() => undefined} />);
+
+    submitSetup();
+
+    await waitFor(() => expect(bootstrapCrossSigning).toHaveBeenCalled());
+    expect(resetKeyBackup).toHaveBeenCalled();
+    expect(userHasCrossSigningKeys).toHaveBeenCalledWith('@me:example.org', true);
+  });
+});
diff --git a/src/app/components/DeviceVerificationSetup.tsx b/src/app/components/DeviceVerificationSetup.tsx
index 1c1911b1bf..e11f5f7705 100644
--- a/src/app/components/DeviceVerificationSetup.tsx
+++ b/src/app/components/DeviceVerificationSetup.tsx
@@ -158,6 +158,12 @@ function SetupVerification({ onComplete, reset }: Readonly<SetupVerificationProp
         const crypto = mx.getCrypto();
         if (!crypto) throw new Error('Unexpected Error! Crypto module not found!');
 
+        if (!reset && (await crypto.userHasCrossSigningKeys(mx.getSafeUserId(), true))) {
+          throw new Error(
+            'This account already has device verification set up. Verify with your recovery key or another device instead.'
+          );
+        }
+
         const recoveryKeyData = await crypto.createRecoveryKeyFromPassphrase(passphrase);
         if (!recoveryKeyData.encodedPrivateKey) {
           throw new Error('Unexpected Error! Failed to create recovery key.');
diff --git a/src/app/components/ManualVerification.test.tsx b/src/app/components/ManualVerification.test.tsx
index 8b89785ce2..1f68e4cac4 100644
--- a/src/app/components/ManualVerification.test.tsx
+++ b/src/app/components/ManualVerification.test.tsx
@@ -7,6 +7,7 @@ import { ManualVerificationTile } from './ManualVerification';
 
 const decodeRecoveryKey = vi.hoisted(() => vi.fn<(key: string) => Uint8Array>());
 const checkKey = vi.hoisted(() => vi.fn<() => Promise<boolean>>());
+const getSecret = vi.hoisted(() => vi.fn<(name: string) => Promise<string | undefined>>());
 const storePrivateKey = vi.hoisted(() => vi.fn<() => void>());
 const processDeviceLists = vi.hoisted(() => vi.fn<() => Promise<void>>());
 const bootstrapCrossSigning = vi.hoisted(() => vi.fn<() => Promise<void>>());
@@ -19,7 +20,7 @@ vi.mock('$hooks/useMatrixClient', () => ({
   useMatrixClient: () => ({
     getSafeUserId: () => '@me:example.org',
     getDeviceId: () => 'DEVICE',
-    secretStorage: { checkKey },
+    secretStorage: { checkKey, get: getSecret },
     getCrypto: () =>
       ({
         processDeviceLists,
@@ -54,6 +55,7 @@ describe('ManualVerificationTile', () => {
     vi.clearAllMocks();
     decodeRecoveryKey.mockReturnValue(recoveryKey);
     checkKey.mockResolvedValue(true);
+    getSecret.mockResolvedValue('stored-key');
     processDeviceLists.mockResolvedValue(undefined);
     bootstrapCrossSigning.mockResolvedValue(undefined);
     bootstrapSecretStorage.mockResolvedValue(undefined);
@@ -84,4 +86,17 @@ describe('ManualVerificationTile', () => {
     await waitFor(() => expect(screen.getByText('Device verified!')).toBeInTheDocument());
     expect(invalidateQueries).toHaveBeenCalledWith({ queryKey: ['device-verification'] });
   });
+
+  it('does not bootstrap when the cross-signing keys are missing from secret storage', async () => {
+    getSecret.mockResolvedValue(undefined);
+    renderTile(new QueryClient());
+
+    submitRecoveryKey('valid-key');
+
+    await waitFor(() =>
+      expect(screen.getByText(/Could not read your cross-signing keys/)).toBeInTheDocument()
+    );
+    expect(bootstrapCrossSigning).not.toHaveBeenCalled();
+    expect(bootstrapSecretStorage).not.toHaveBeenCalled();
+  });
 });
diff --git a/src/app/components/ManualVerification.tsx b/src/app/components/ManualVerification.tsx
index 3765e4fe1d..a52c2fc7d8 100644
--- a/src/app/components/ManualVerification.tsx
+++ b/src/app/components/ManualVerification.tsx
@@ -11,6 +11,7 @@ import { storePrivateKey } from '$client/secretStorageKeys';
 import { stopPropagation } from '$utils/keyboard';
 import { useMatrixClient } from '$hooks/useMatrixClient';
 import { useRefreshDeviceVerificationStatus } from '$hooks/useDeviceVerificationStatus';
+import { restoreCrossSigningFromSecretStorage } from '$utils/matrix-crypto';
 import { AsyncStatus, useAsyncCallback } from '$hooks/useAsyncCallback';
 import { AsyncError } from '$components/AsyncError';
 import { SettingTile } from './setting-tile';
@@ -130,7 +131,7 @@ export function ManualVerificationTile({
       storePrivateKey(secretStorageKeyId, recoveryKey);
 
       await crypto.processDeviceLists({ changed: [mx.getSafeUserId()] });
-      await crypto.bootstrapCrossSigning({});
+      await restoreCrossSigningFromSecretStorage(mx, crypto);
       await crypto.bootstrapSecretStorage({});
 
       await crypto.loadSessionBackupPrivateKeyFromSecretStorage();
diff --git a/src/app/features/settings/devices/Devices.tsx b/src/app/features/settings/devices/Devices.tsx
index 43cd48f461..deebd4371e 100644
--- a/src/app/features/settings/devices/Devices.tsx
+++ b/src/app/features/settings/devices/Devices.tsx
@@ -13,7 +13,7 @@ import {
   VerificationStatus,
 } from '$hooks/useDeviceVerificationStatus';
 import { useSecretStorageDefaultKeyId, useSecretStorageKeyContent } from '$hooks/useSecretStorage';
-import { useCrossSigningActive } from '$hooks/useCrossSigning';
+import { CrossSigningStatus, useCrossSigningStatus } from '$hooks/useCrossSigning';
 import { BackupRestoreTile } from '$components/BackupRestore';
 import { LocalBackup } from './LocalBackup';
 import { DeviceLogoutBtn, DeviceKeyDetails, DeviceTile, DeviceTilePlaceholder } from './DeviceTile';
@@ -41,7 +41,8 @@ type DevicesProps = {
 export function Devices({ requestBack, requestClose }: DevicesProps) {
   const mx = useMatrixClient();
   const crypto = mx.getCrypto();
-  const crossSigningActive = useCrossSigningActive();
+  const crossSigningStatus = useCrossSigningStatus();
+  const crossSigningActive = crossSigningStatus === CrossSigningStatus.Active;
   const [devices, refreshDeviceList] = useDeviceList();
 
   useEffect(() => {
@@ -90,7 +91,10 @@ export function Devices({ requestBack, requestClose }: DevicesProps) {
                     description="To verify device identity and grant access to encrypted messages."
                     after={
                       <>
-                        <EnableVerification visible={!crossSigningActive} />
+                        <EnableVerification
+                          visible={!crossSigningActive}
+                          loading={crossSigningStatus === CrossSigningStatus.Unknown}
+                        />
                         {crossSigningActive && (
                           <Box gap="200" alignItems="Center">
                             <VerificationStatusBadge
diff --git a/src/app/features/settings/devices/Verification.tsx b/src/app/features/settings/devices/Verification.tsx
index 2fcecb0777..f3dd405b7e 100644
--- a/src/app/features/settings/devices/Verification.tsx
+++ b/src/app/features/settings/devices/Verification.tsx
@@ -281,8 +281,9 @@ export function VerifyOtherDeviceTile({ crypto, deviceId }: VerifyOtherDeviceTil
 
 type EnableVerificationProps = {
   visible: boolean;
+  loading?: boolean;
 };
-export function EnableVerification({ visible }: EnableVerificationProps) {
+export function EnableVerification({ visible, loading }: EnableVerificationProps) {
   const [open, setOpen] = useState(false);
 
   const handleCancel = useCallback(() => setOpen(false), []);
@@ -290,7 +291,13 @@ export function EnableVerification({ visible }: EnableVerificationProps) {
   return (
     <>
       {visible && (
-        <Button size="300" radii="300" onClick={() => setOpen(true)}>
+        <Button
+          size="300"
+          radii="300"
+          onClick={() => setOpen(true)}
+          disabled={loading}
+          before={loading && <Spinner size="100" variant="Primary" fill="Solid" />}
+        >
           <Text as="span" size="B300">
             Enable
           </Text>
diff --git a/src/app/hooks/useCrossSigning.ts b/src/app/hooks/useCrossSigning.ts
index 583d78dd15..7ec8768ad6 100644
--- a/src/app/hooks/useCrossSigning.ts
+++ b/src/app/hooks/useCrossSigning.ts
@@ -1,10 +1,38 @@
+import { useQuery } from '@tanstack/react-query';
 import type { SecretAccountData } from '$types/matrix/accountData';
 
 import { useAccountData } from './useAccountData';
+import { useMatrixClient } from './useMatrixClient';
 
-export const useCrossSigningActive = (): boolean => {
+export enum CrossSigningStatus {
+  Unknown,
+  Active,
+  Inactive,
+}
+
+// `getAccountData` reads the local store, so an unsynced account is indistinguishable from one
+// that never set cross-signing up, and setting it up again resets it.
+export const useCrossSigningStatus = (): CrossSigningStatus => {
+  const mx = useMatrixClient();
   const masterEvent = useAccountData('m.cross_signing.master');
-  const content = masterEvent?.getContent<SecretAccountData>();
+  const storedLocally = !!masterEvent?.getContent<SecretAccountData>();
+
+  const { data } = useQuery({
+    queryKey: ['cross-signing-keys', mx.getSafeUserId()],
+    queryFn: async () => {
+      const crypto = mx.getCrypto();
+      if (!crypto) return null;
+      // An untracked own user reports false unless the key list is downloaded.
+      return crypto.userHasCrossSigningKeys(mx.getSafeUserId(), true);
+    },
+    enabled: !storedLocally,
+    staleTime: 60000,
+  });
 
-  return !!content;
+  if (storedLocally) return CrossSigningStatus.Active;
+  if (typeof data !== 'boolean') return CrossSigningStatus.Unknown;
+  return data ? CrossSigningStatus.Active : CrossSigningStatus.Inactive;
 };
+
+export const useCrossSigningActive = (): boolean =>
+  useCrossSigningStatus() === CrossSigningStatus.Active;
diff --git a/src/app/utils/matrix-crypto.ts b/src/app/utils/matrix-crypto.ts
index 23ba678eb2..5bd9514a36 100644
--- a/src/app/utils/matrix-crypto.ts
+++ b/src/app/utils/matrix-crypto.ts
@@ -1,4 +1,4 @@
-import type { CryptoApi } from '$types/matrix-sdk';
+import type { CryptoApi, MatrixClient } from '$types/matrix-sdk';
 
 export const verifiedDevice = async (
   api: CryptoApi,
@@ -11,3 +11,32 @@ export const verifiedDevice = async (
 
   return status.crossSigningVerified;
 };
+
+const CROSS_SIGNING_SECRETS = [
+  'm.cross_signing.master',
+  'm.cross_signing.self_signing',
+  'm.cross_signing.user_signing',
+];
+
+// `bootstrapCrossSigning` mints a new identity and writes it to 4S when it cannot read the keys,
+// and account data missing from the local store reads as "no keys".
+export const restoreCrossSigningFromSecretStorage = async (
+  mx: MatrixClient,
+  crypto: CryptoApi
+): Promise<void> => {
+  const storedKeys = await Promise.all(
+    CROSS_SIGNING_SECRETS.map((secretName) => mx.secretStorage.get(secretName))
+  );
+
+  if (storedKeys.some((key) => !key)) {
+    throw new Error(
+      'Could not read your cross-signing keys from secret storage. Wait for the sync to finish and try again.'
+    );
+  }
+
+  await crypto.bootstrapCrossSigning({
+    authUploadDeviceSigningKeys: async () => {
+      throw new Error('Refusing to replace your cross-signing identity to verify this device.');
+    },
+  });
+};
diff --git a/src/client/presenceSync.ts b/src/client/presenceSync.ts
index 684f328ea3..02f08c27f0 100644
--- a/src/client/presenceSync.ts
+++ b/src/client/presenceSync.ts
@@ -120,6 +120,9 @@ export class PresenceSyncManager {
           { abortSignal: signal }
         );
 
+        // Emitting after teardown drives SDK listeners into a crypto store that is closing.
+        if (signal.aborted || this.disposed || !this.mx.clientRunning) return;
+
         this.processPresence(response);
         this.syncToken = response.next_batch;