diff --git a/litellm/cost_calculator.py b/litellm/cost_calculator.py
index d6f9adb00..0fab08625 100644
--- a/litellm/cost_calculator.py
+++ b/litellm/cost_calculator.py
@@ -665,7 +665,7 @@ def completion_cost(
 
         if custom_llm_provider is not None and custom_llm_provider == "vertex_ai":
             # Calculate the prompt characters + response characters
-            if len("messages") > 0:
+            if len(messages) > 0:
                 prompt_string = litellm.utils.get_formatted_prompt(
                     data={"messages": messages}, call_type="completion"
                 )