diff --git a/tests/test_litellm/llms/vertex_ai/batches/test_transformation.py b/tests/test_litellm/llms/vertex_ai/batches/test_transformation.py
index 232c6413e78..e6126b02790 100644
--- a/tests/test_litellm/llms/vertex_ai/batches/test_transformation.py
+++ b/tests/test_litellm/llms/vertex_ai/batches/test_transformation.py
@@ -17,9 +17,9 @@ from unittest.mock import patch
 
 import pytest
 
-
 from litellm.llms.vertex_ai.batches.transformation import (  # noqa: E402
     VertexAIBatchTransformation,
+    vertex_prompt_tokens_details,
 )
 from litellm.llms.vertex_ai.common_utils import (  # noqa: E402
     VertexAIError,
@@ -41,6 +41,22 @@ ENDPOINT_INPUT_FILE = (
 )
 
 
+def test_vertex_prompt_tokens_details_rejects_malformed_details():
+    assert vertex_prompt_tokens_details({"promptTokensDetails": [1]}) is None
+    assert vertex_prompt_tokens_details({"promptTokensDetails": [{"modality": "AUDIO"}]}) is None
+    assert (
+        vertex_prompt_tokens_details(
+            {
+                "promptTokensDetails": [
+                    {"modality": "AUDIO", "tokenCount": 1},
+                    "malformed",
+                ]
+            }
+        )
+        is None
+    )
+
+
 # =========================================================================== #
 # transform_openai_batch_request_to_vertex_ai_batch_request
 # =========================================================================== #