diff --git a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
index ae2faeccdd8..bf2a8240652 100644
--- a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
+++ b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
@@ -367,12 +367,12 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
         """
         Map OpenAI service_tier (string) to Gemini serviceTier.
         'auto' maps to 'priority'.
-        Other values are passed blindly.
+        Other values are passed lowercased.
         """
         if value == "auto":
             optional_params["service_tier"] = "priority"
         else:
-            optional_params["service_tier"] = value
+            optional_params["service_tier"] = value.lower()
 
     def _transform_computer_use_config(self, computer_use_config: dict) -> dict:
         """
diff --git a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
index f0c899d35ea..48f740cda8f 100644
--- a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
+++ b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
@@ -3688,7 +3688,7 @@ def test_vertex_ai_service_tier_in_map_openai_params():
         drop_params=True,
     )
 
-    assert result["service_tier"] == "FLEX"
+    assert result["service_tier"] == "flex"
 
     # Test auto -> priority
     optional_params_auto = {}