diff --git a/autogen/agentchat/conversable_agent.py b/autogen/agentchat/conversable_agent.py
index 838af6e7df7..3f19a1dba61 100644
--- a/autogen/agentchat/conversable_agent.py
+++ b/autogen/agentchat/conversable_agent.py
@@ -168,7 +168,6 @@ def __init__(
         )
         self._default_auto_reply = default_auto_reply
         self._reply_func_list = []
-        self._ignore_async_func_in_sync_chat_list = []
         self._human_input = []
         self.reply_at_receive = defaultdict(bool)
         self.register_reply([Agent, None], ConversableAgent.generate_oai_reply)
@@ -342,10 +341,9 @@ def reply_func(
                 "config": copy.copy(config),
                 "init_config": config,
                 "reset_config": reset_config,
+                "ignore_async_in_sync_chat": ignore_async_in_sync_chat and inspect.iscoroutinefunction(reply_func),
             },
         )
-        if ignore_async_in_sync_chat and inspect.iscoroutinefunction(reply_func):
-            self._ignore_async_func_in_sync_chat_list.append(reply_func)
 
     @staticmethod
     def _summary_from_nested_chats(
@@ -843,9 +841,9 @@ def _raise_exception_on_async_reply_functions(self) -> None:
         Raises:
             RuntimeError: if any async reply functions are registered.
         """
-        reply_functions = {f["reply_func"] for f in self._reply_func_list}.difference(
-            self._ignore_async_func_in_sync_chat_list
-        )
+        reply_functions = {
+            f["reply_func"] for f in self._reply_func_list if not f.get("ignore_async_in_sync_chat", False)
+        }
 
         async_reply_functions = [f for f in reply_functions if inspect.iscoroutinefunction(f)]
         if async_reply_functions != []: