diff --git a/src/alta-client.js b/src/alta-client.js
index 6ea04ce..f2a53a1 100644
--- a/src/alta-client.js
+++ b/src/alta-client.js
@@ -98,15 +98,11 @@ function enforceResponseSize(data, headers, maxBytes) {
 }
 
 function safeTransportError(operation, error, cookie) {
-  if (error && typeof error === 'object' && typeof error.code === 'string' && error.code.startsWith('ALTA_')) {
-    return error;
-  }
   const formatted = formatAltaError(operation, error, { secrets: [cookie, `va=${cookie}`] });
-  const safe = altaError(formatted.code, formatted.message, {
+  return altaError(formatted.code, formatted.message, {
     status: formatted.status,
     timeout: formatted.timeout,
   });
-  return safe;
 }
 
 class AltaClient {
diff --git a/test/alta-client.test.js b/test/alta-client.test.js
index dfc5f1f..b33c295 100644
--- a/test/alta-client.test.js
+++ b/test/alta-client.test.js
@@ -167,6 +167,57 @@ test('rejects malformed response envelopes, JSON, status and endpoint data shape
   await assert.rejects(authClient.getAuthInfo(), { code: 'INVALID_ALTA_RESPONSE_DATA' });
 });
 
+test('returns a fresh allowlisted error when transport throws an ALTA error with secret-bearing fields', async () => {
+  const source = Object.assign(new Error(`Alta request failed for va=${SENTINEL}`), {
+    code: 'ALTA_TRANSPORT_FAILURE',
+    status: 503,
+    timeout: true,
+    config: { headers: { Cookie: `va=${SENTINEL}` }, data: SENTINEL },
+    request: { headers: { Cookie: `va=${SENTINEL}` }, body: SENTINEL },
+    response: { status: 502, headers: { 'set-cookie': `va=${SENTINEL}` }, data: SENTINEL },
+    body: SENTINEL,
+  });
+  const client = new AltaClient({
+    sessionStore: readyStore(),
+    transport: async () => { throw source; },
+  });
+
+  const caught = await client.getDevices().catch((error) => error);
+  assert.notEqual(caught, source);
+  assert.equal(caught.code, 'ALTA_TRANSPORT_FAILURE');
+  assert.equal(caught.message, 'Alta request failed for va=[REDACTED]');
+  assert.equal(caught.status, 502);
+  assert.equal(caught.timeout, true);
+  assert.deepEqual(Object.keys(caught).sort(), ['code', 'status', 'timeout']);
+  for (const field of ['config', 'request', 'response', 'headers', 'data', 'body']) {
+    assert.equal(field in caught, false, field);
+  }
+  assert.doesNotMatch(JSON.stringify(caught), new RegExp(SENTINEL));
+});
+
+test('safely formats a transport error whose code getter throws a secret', async () => {
+  const source = new Error('Transport failed safely');
+  Object.defineProperty(source, 'code', {
+    enumerable: true,
+    get() { throw new Error(SENTINEL); },
+  });
+  source.config = { headers: { Cookie: `va=${SENTINEL}` } };
+  const client = new AltaClient({
+    sessionStore: readyStore(),
+    transport: async () => { throw source; },
+  });
+
+  const caught = await client.getDevices().catch((error) => error);
+  assert.notEqual(caught, source);
+  assert.equal(caught.code, 'ALTA_ERROR');
+  assert.equal(caught.message, 'Transport failed safely');
+  assert.equal(caught.status, null);
+  assert.equal(caught.timeout, false);
+  assert.deepEqual(Object.keys(caught).sort(), ['code', 'status', 'timeout']);
+  assert.equal('config' in caught, false);
+  assert.doesNotMatch(JSON.stringify(caught), new RegExp(SENTINEL));
+});
+
 test('revalidates the stored origin before each request', async () => {
   const store = { requireSession: () => Object.freeze({ origin: 'https://evil.example', cookie: SENTINEL }) };
   let called = false;