diff --git a/temporalio/contrib/openai_agents/_openai_runner.py b/temporalio/contrib/openai_agents/_openai_runner.py
index 6f0d74064..94a079fd5 100644
--- a/temporalio/contrib/openai_agents/_openai_runner.py
+++ b/temporalio/contrib/openai_agents/_openai_runner.py
@@ -1,3 +1,4 @@
+import json
 import typing
 from dataclasses import replace
 from typing import Any, Union
@@ -13,6 +14,7 @@
     TResponseInputItem,
 )
 from agents.run import DEFAULT_AGENT_RUNNER, DEFAULT_MAX_TURNS, AgentRunner
+from pydantic_core import to_json
 
 from temporalio import workflow
 from temporalio.contrib.openai_agents._model_parameters import ModelActivityParameters
@@ -57,6 +59,11 @@ async def run(
                 "Temporal OpenAI agent does not support on demand MCP servers."
             )
 
+        # workaround for https://github.com/pydantic/pydantic/issues/9541
+        # ValidatorIterator returned
+        input_json = to_json(input)
+        input = json.loads(input_json)
+
         context = kwargs.get("context")
         max_turns = kwargs.get("max_turns", DEFAULT_MAX_TURNS)
         hooks = kwargs.get("hooks")