diff --git a/litellm/proxy/common_request_processing.py b/litellm/proxy/common_request_processing.py
index ef08aa2e22..80c115c1bd 100644
--- a/litellm/proxy/common_request_processing.py
+++ b/litellm/proxy/common_request_processing.py
@@ -1792,13 +1792,18 @@ class ProxyBaseLLMRequestProcessing:
 
         body_bytes = await response.aread()  # type: ignore[union-attr]
         parsed = _json.loads(body_bytes)
-        parsed = await proxy_logging_obj.post_call_success_hook(
+        processed = await proxy_logging_obj.post_call_success_hook(
             data=self.data,
             user_api_key_dict=user_api_key_dict,
             response=parsed,
         )
+        content = (
+            _json.dumps(processed).encode()
+            if isinstance(processed, dict)
+            else body_bytes
+        )
         return Response(
-            content=_json.dumps(parsed).encode(),
+            content=content,
             status_code=response_status,
             media_type="application/json",
             headers=response_headers,
diff --git a/tests/test_litellm/proxy/test_common_request_processing.py b/tests/test_litellm/proxy/test_common_request_processing.py
index e238047582..7765dde82b 100644
--- a/tests/test_litellm/proxy/test_common_request_processing.py
+++ b/tests/test_litellm/proxy/test_common_request_processing.py
@@ -2414,6 +2414,49 @@ class TestAllmPassthroughRoutePostCallGuardrails:
 
         ProxyLogging._callback_capabilities_cache.clear()
 
+    @pytest.mark.asyncio
+    async def test_non_dict_hook_return_falls_back_to_original_body(self, monkeypatch):
+        """
+        When post_call_success_hook returns a non-dict (e.g. a non-serializable
+        object), the JSON branch must return the original body bytes unchanged
+        rather than raising a TypeError from json.dumps.
+        """
+        import json
+
+        original = {
+            "output": {"message": {"role": "assistant", "content": [{"text": "hi"}]}},
+            "stopReason": "end_turn",
+        }
+        httpx_response = httpx.Response(
+            status_code=200,
+            content=json.dumps(original).encode(),
+            headers={"content-type": "application/json"},
+        )
+
+        async def non_dict_hook(data, user_api_key_dict, response):
+            return object()
+
+        cb = self._make_guardrail_cb()
+        monkeypatch.setattr(litellm, "callbacks", [cb])
+        ProxyLogging._callback_capabilities_cache.clear()
+
+        proxy_logging_obj = ProxyLogging(user_api_key_cache=MagicMock())
+        monkeypatch.setattr(proxy_logging_obj, "post_call_success_hook", non_dict_hook)
+
+        with patch.object(ProxyBaseLLMRequestProcessing, "_has_post_call_guardrails", return_value=True):
+            processing_obj = ProxyBaseLLMRequestProcessing(data={})
+            result = await processing_obj._handle_non_streaming_allm_passthrough_route(
+                response=httpx_response,
+                proxy_logging_obj=proxy_logging_obj,
+                user_api_key_dict=MagicMock(spec=UserAPIKeyAuth),
+                custom_headers={},
+            )
+
+        assert isinstance(result, Response)
+        assert json.loads(result.body) == original
+
+        ProxyLogging._callback_capabilities_cache.clear()
+
     @pytest.mark.asyncio
     async def test_no_aread_when_no_post_call_guardrails(self, monkeypatch):
         """