diff --git a/litellm/cost_calculator.py b/litellm/cost_calculator.py
index 6eec8d3cd..a3cb847a4 100644
--- a/litellm/cost_calculator.py
+++ b/litellm/cost_calculator.py
@@ -490,10 +490,18 @@ def completion_cost(
             isinstance(completion_response, BaseModel)
             or isinstance(completion_response, dict)
         ):  # tts returns a custom class
-            if isinstance(completion_response, BaseModel) and not isinstance(
-                completion_response, litellm.Usage
+
+            usage_obj: Optional[Union[dict, litellm.Usage]] = completion_response.get(
+                "usage", {}
+            )
+            if isinstance(usage_obj, BaseModel) and not isinstance(
+                usage_obj, litellm.Usage
             ):
-                completion_response = litellm.Usage(**completion_response.model_dump())
+                setattr(
+                    completion_response,
+                    "usage",
+                    litellm.Usage(**usage_obj.model_dump()),
+                )
             # get input/output tokens from completion_response
             prompt_tokens = completion_response.get("usage", {}).get("prompt_tokens", 0)
             completion_tokens = completion_response.get("usage", {}).get(
diff --git a/litellm/tests/test_custom_logger.py b/litellm/tests/test_custom_logger.py
index e3407c9e1..465012bff 100644
--- a/litellm/tests/test_custom_logger.py
+++ b/litellm/tests/test_custom_logger.py
@@ -1,11 +1,17 @@
 ### What this tests ####
-import sys, os, time, inspect, asyncio, traceback
+import asyncio
+import inspect
+import os
+import sys
+import time
+import traceback
+
 import pytest
 
 sys.path.insert(0, os.path.abspath("../.."))
 
-from litellm import completion, embedding
 import litellm
+from litellm import completion, embedding
 from litellm.integrations.custom_logger import CustomLogger
 
 
@@ -201,7 +207,7 @@ def test_async_custom_handler_stream():
         print("complete_streaming_response: ", complete_streaming_response)
         assert response_in_success_handler == complete_streaming_response
     except Exception as e:
-        pytest.fail(f"Error occurred: {e}")
+        pytest.fail(f"Error occurred: {e}\n{traceback.format_exc()}")
 
 
 # test_async_custom_handler_stream()
@@ -457,11 +463,11 @@ async def test_cost_tracking_with_caching():
 
 
 def test_redis_cache_completion_stream():
-    from litellm import Cache
-
     # Important Test - This tests if we can add to streaming cache, when custom callbacks are set
     import random
 
+    from litellm import Cache
+
     try:
         print("\nrunning test_redis_cache_completion_stream")
         litellm.set_verbose = True