diff --git a/libs/langchain_v1/langchain/agents/structured_output.py b/libs/langchain_v1/langchain/agents/structured_output.py
index ada304b8d3f..336c4b48d33 100644
--- a/libs/langchain_v1/langchain/agents/structured_output.py
+++ b/libs/langchain_v1/langchain/agents/structured_output.py
@@ -198,6 +198,7 @@ class ToolOutput(Generic[SchemaT]):
 
     def __init__(
         self,
+        *,
         schema: type[SchemaT],
         tool_message_content: str | None = None,
         handle_errors: bool