diff --git a/python/packages/autogen-core/src/autogen_core/_single_threaded_agent_runtime.py b/python/packages/autogen-core/src/autogen_core/_single_threaded_agent_runtime.py
index 307cdd863e..5f56364416 100644
--- a/python/packages/autogen-core/src/autogen_core/_single_threaded_agent_runtime.py
+++ b/python/packages/autogen-core/src/autogen_core/_single_threaded_agent_runtime.py
@@ -362,6 +362,7 @@ class SingleThreadedAgentRuntime(AgentRuntime):
             future = asyncio.get_event_loop().create_future()
             if recipient.type not in self._known_agent_names:
                 future.set_exception(Exception("Recipient not found"))
+                return await future
 
             content = message.__dict__ if hasattr(message, "__dict__") else message
             logger.info(f"Sending message of type {type(message).__name__} to {recipient.type}: {content}")