diff --git a/clients/python/src/zb_mom_ww_mxgateway/session.py b/clients/python/src/zb_mom_ww_mxgateway/session.py
index 78f75aa..8a8d3bf 100644
--- a/clients/python/src/zb_mom_ww_mxgateway/session.py
+++ b/clients/python/src/zb_mom_ww_mxgateway/session.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from collections.abc import AsyncIterator, Sequence
+from typing import Any
 
 from .auth import redact_secret
 from .errors import MalformedReplyError, MxGatewayError, ensure_mxaccess_success
@@ -943,22 +944,26 @@ def _redact_error(error: MxGatewayError, secrets: Sequence[str | None]) -> None:
         error.raw_reply = _redact_reply(error.raw_reply, scrubbed)
 
 
-def _redact_reply(reply: pb.MxCommandReply, secrets: Sequence[str]) -> pb.MxCommandReply:
+def _redact_reply(reply: Any, secrets: Sequence[str]) -> Any:
     """Return a deep copy of *reply* with credential text scrubbed from diagnostics.
 
     Operates on a clone so the caller's original reply object is never mutated.
     Only the free-text diagnostic fields that can echo a client-supplied secret
     are scrubbed; the structured/enum fields the gateway itself sets are left as-is.
+    Works for any reply message (``MxCommandReply``, ``AcknowledgeAlarmReply``, ...):
+    each field is scrubbed only when the message type declares it.
     """
     clone = type(reply)()
     clone.CopyFrom(reply)
-    if clone.protocol_status.message:
+    fields = clone.DESCRIPTOR.fields_by_name
+    if "protocol_status" in fields and clone.protocol_status.message:
         clone.protocol_status.message = redact_secret(clone.protocol_status.message, secrets)
-    if clone.diagnostic_message:
+    if "diagnostic_message" in fields and clone.diagnostic_message:
         clone.diagnostic_message = redact_secret(clone.diagnostic_message, secrets)
-    for status in clone.statuses:
-        if status.diagnostic_text:
-            status.diagnostic_text = redact_secret(status.diagnostic_text, secrets)
+    if "statuses" in fields:
+        for status in clone.statuses:
+            if status.diagnostic_text:
+                status.diagnostic_text = redact_secret(status.diagnostic_text, secrets)
     return clone
 
 
diff --git a/clients/python/tests/test_alarms.py b/clients/python/tests/test_alarms.py
index 4319139..d8a6e73 100644
--- a/clients/python/tests/test_alarms.py
+++ b/clients/python/tests/test_alarms.py
@@ -74,6 +74,40 @@ async def test_acknowledge_alarm_error_redacts_operator_password() -> None:
     assert "pw-secret" not in str(excinfo.value)
 
 
+@pytest.mark.asyncio
+async def test_acknowledge_alarm_protocol_failure_redacts_operator_password() -> None:
+    from zb_mom_ww_mxgateway.errors import MxGatewayError
+
+    stub = FakeGatewayStub()
+    stub.acknowledge_alarm.replies = [
+        pb.AcknowledgeAlarmReply(
+            protocol_status=pb.ProtocolStatus(
+                code=pb.PROTOCOL_STATUS_CODE_INVALID_REQUEST,
+                message="rejected credential pw-secret",
+            ),
+        ),
+    ]
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+
+    with pytest.raises(MxGatewayError) as excinfo:
+        await client.acknowledge_alarm(
+            pb.AcknowledgeAlarmRequest(
+                alarm_full_reference="Tank01.Level.HiHi",
+                operator_user="alice",
+                operator_password="pw-secret",
+            ),
+        )
+
+    assert "pw-secret" not in str(excinfo.value)
+    raw = excinfo.value.raw_reply
+    assert isinstance(raw, pb.AcknowledgeAlarmReply)
+    assert "pw-secret" not in raw.protocol_status.message
+    assert "pw-secret" not in str(raw)
+
+
 @pytest.mark.asyncio
 async def test_acknowledge_alarm_unauthenticated_raises_typed_error() -> None:
     stub = FakeGatewayStub()