diff --git a/litellm/proxy/google_endpoints/endpoints.py b/litellm/proxy/google_endpoints/endpoints.py
index 61d1232ccec..3e63a15e128 100644
--- a/litellm/proxy/google_endpoints/endpoints.py
+++ b/litellm/proxy/google_endpoints/endpoints.py
@@ -1,7 +1,7 @@
 from collections.abc import Mapping
 from itertools import chain
 from types import MappingProxyType
-from typing import Final
+from typing import Final, cast
 
 from fastapi import APIRouter, Depends, HTTPException, Request, Response
 from fastapi.responses import JSONResponse, ORJSONResponse
@@ -37,7 +37,7 @@ class _GoogleCountTokensSystemInstruction(BaseModel):
     @field_validator("parts", mode="before")
     @classmethod
     def normalize_parts(cls, parts: object) -> object:
-        return (parts,) if isinstance(parts, Mapping) else parts
+        return (cast(object, parts),) if isinstance(parts, Mapping) else parts
 
 
 class _GoogleCountTokensFunctionDeclaration(BaseModel):