diff --git a/litellm/llms/vertex_ai/common_utils.py b/litellm/llms/vertex_ai/common_utils.py
index d72fc88052d..d3e79ce3fdd 100644
--- a/litellm/llms/vertex_ai/common_utils.py
+++ b/litellm/llms/vertex_ai/common_utils.py
@@ -1170,7 +1170,11 @@ class VertexAITokenCounter(BaseTokenCounter):
             )
 
             resolved_contents: Final = (
-                contents if contents is not None else _gemini_convert_messages_with_history(messages=messages or [])
+                contents
+                if contents is not None
+                else _gemini_convert_messages_with_history(
+                    messages=messages or []  # mutable-ok: fallback for None messages; helper signature requires list
+                )
             )
 
             count_tokens_params: Final = {