diff --git a/google/genai/_mcp_utils.py b/google/genai/_mcp_utils.py
index 3d4ae2a17..b2c70fa14 100644
--- a/google/genai/_mcp_utils.py
+++ b/google/genai/_mcp_utils.py
@@ -143,7 +143,7 @@ def _filter_to_supported_schema(
 
   filtered_schema: dict[str, Any] = {}
   for field_name, field_value in schema.items():
-    if field_name in schema_field_names:
+    if field_name in schema_field_names and isinstance(field_value, dict):
       filtered_schema[field_name] = _filter_to_supported_schema(field_value)
     elif field_name in list_schema_field_names:
       filtered_schema[field_name] = [