diff --git a/basedpyright-code-budget.json b/basedpyright-code-budget.json
index 83d087efad4..9997e5dc0c6 100644
--- a/basedpyright-code-budget.json
+++ b/basedpyright-code-budget.json
@@ -123,7 +123,7 @@
     "limit": 5
   },
   "reportUnnecessaryIsInstance": {
-    "limit": 824
+    "limit": 823
   },
   "reportUntypedBaseClass": {
     "limit": 0
diff --git a/litellm/llms/openai/responses/guardrail_translation/handler.py b/litellm/llms/openai/responses/guardrail_translation/handler.py
index 7fbc43c8783..caa20207a15 100644
--- a/litellm/llms/openai/responses/guardrail_translation/handler.py
+++ b/litellm/llms/openai/responses/guardrail_translation/handler.py
@@ -118,9 +118,13 @@ _TOOL_TYPES_NOT_SENT_TO_GUARDRAIL: Final = frozenset(
 _NAMESPACE_MEMBERS: Final = TypeAdapter(tuple[Mapping[str, object], ...])
 
 
-def _namespace_members(tool: Mapping[str, object]) -> tuple[Mapping[str, object], ...]:
+def _namespace_members(tool: Mapping[str, object]) -> tuple[Mapping[str, object], ...] | None:
+    """``None`` when the namespace has no member list and is flattened to one function named after it."""
+    raw_members: Final = tool.get("tools")
+    if not isinstance(raw_members, Sequence) or isinstance(raw_members, (str, bytes)):
+        return None
     try:
-        return _NAMESPACE_MEMBERS.validate_python(tool.get("tools") or ())
+        return _NAMESPACE_MEMBERS.validate_python(raw_members)
     except ValidationError:
         return ()
 
@@ -133,17 +137,21 @@ def _qualified_member_name(namespace: str, member: Mapping[str, object]) -> str:
     return f"{namespace}__{member.get('name') or ''}"
 
 
+def _namespace_function_names(tool: Mapping[str, object]) -> tuple[str, ...]:
+    namespace: Final = str(tool.get("name") or "")
+    members: Final = _namespace_members(tool)
+    if members is None:
+        return (namespace,)
+    return tuple(_qualified_member_name(namespace, member) for member in members if _is_function_member(member))
+
+
 def _flattened_function_names(tools: Sequence[Mapping[str, object]]) -> tuple[str, ...]:
     """Names the guardrail sees for ``tools`` once flattened to Chat Completions format."""
     top_level: Final = tuple(
         str(tool.get("name") or "") for tool in tools if tool.get("type") in ("function", "custom")
     )
     nested: Final = tuple(
-        _qualified_member_name(str(tool.get("name") or ""), member)
-        for tool in tools
-        if tool.get("type") == "namespace"
-        for member in _namespace_members(tool)
-        if _is_function_member(member)
+        name for tool in tools if tool.get("type") == "namespace" for name in _namespace_function_names(tool)
     )
     return top_level + nested
 
@@ -153,6 +161,8 @@ def _merge_namespace_tool(
 ) -> Mapping[str, object] | None:
     namespace: Final = str(tool.get("name") or "")
     members: Final = _namespace_members(tool)
+    if members is None:
+        return tool if namespace in remapped_functions else None
     surviving: Final = tuple(
         member
         for member in members
diff --git a/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py b/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
index b4e206fbc92..7e624f39c53 100644
--- a/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
+++ b/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
@@ -1388,6 +1388,24 @@ class TestOpenAIResponsesHandlerNamespaceTools:
         assert result["tools"][2]["name"] == "injected_tool"
         assert not any(t["name"].startswith("mcp__confluence__") for t in result["tools"])
 
+    @pytest.mark.asyncio
+    async def test_unchanged_guardrail_leaves_custom_mcp_and_memberless_namespace_tools_as_is(self):
+        handler = OpenAIResponsesHandler()
+        tools = [
+            {"type": "custom", "name": "apply_patch", "description": "Apply a patch"},
+            {"type": "mcp", "server_label": "docs", "server_url": "https://mcp.example.com"},
+            {"type": "namespace", "name": "mcp__flat", "description": "Flattened to one function"},
+        ]
+        data = {
+            "input": [{"role": "user", "content": "fetch page 1", "type": "message"}],
+            "tools": [dict(t) for t in tools],
+            "model": "gpt-5.3-codex",
+        }
+
+        result = await handler.process_input_messages(data, MockPassThroughGuardrail(guardrail_name="test"))
+
+        assert result["tools"] == tools
+
     @pytest.mark.asyncio
     async def test_guardrail_can_still_drop_a_single_namespace_member(self):
         handler = OpenAIResponsesHandler()
diff --git a/type-discipline-budget.json b/type-discipline-budget.json
index 1a9642c49ae..07bc874880f 100644
--- a/type-discipline-budget.json
+++ b/type-discipline-budget.json
@@ -1,9 +1,9 @@
 {
   "LIT001": {
-    "limit": 22358
+    "limit": 22352
   },
   "LIT002": {
-    "limit": 26775
+    "limit": 26774
   },
   "LIT003": {
     "limit": 269
@@ -27,7 +27,7 @@
     "limit": 0
   },
   "LIT010": {
-    "limit": 16505
+    "limit": 16504
   },
   "LIT011": {
     "limit": 5535