diff --git a/src/controlflow/agents/agent.py b/src/controlflow/agents/agent.py
index ef1be609..e14ee063 100644
--- a/src/controlflow/agents/agent.py
+++ b/src/controlflow/agents/agent.py
@@ -238,7 +238,7 @@ async def run_async(
         objective: str,
         *,
         turn_strategy: Optional["TurnStrategy"] = None,
-        handlers: Optional[list["Handler"]] = None,
+        handlers: Optional[list[Union["Handler", "AsyncHandler"]]] = None,
         **task_kwargs,
     ):
         return await controlflow.run_async(
diff --git a/src/controlflow/events/orchestrator_events.py b/src/controlflow/events/orchestrator_events.py
index 6c07fef1..932fe8de 100644
--- a/src/controlflow/events/orchestrator_events.py
+++ b/src/controlflow/events/orchestrator_events.py
@@ -1,4 +1,7 @@
-from typing import Literal
+from dataclasses import Field
+from typing import Annotated, Literal
+
+from pydantic.functional_serializers import PlainSerializer
 
 from controlflow.agents.agent import Agent
 from controlflow.events.base import UnpersistedEvent
@@ -21,7 +24,7 @@ class OrchestratorError(UnpersistedEvent):
     event: Literal["orchestrator-error"] = "orchestrator-error"
     persist: bool = False
     orchestrator: Orchestrator
-    error: Exception
+    error: Annotated[Exception, PlainSerializer(lambda x: str(x), return_type=str)]
 
 
 class AgentTurnStart(UnpersistedEvent):