diff --git a/api/core/agent/cot_agent_runner.py b/api/core/agent/cot_agent_runner.py
index 565fb42478..6cb1077126 100644
--- a/api/core/agent/cot_agent_runner.py
+++ b/api/core/agent/cot_agent_runner.py
@@ -197,7 +197,7 @@ class CotAgentRunner(BaseAgentRunner, ABC):
                             final_answer = scratchpad.action.action_input
                         else:
                             final_answer = f"{scratchpad.action.action_input}"
-                    except json.JSONDecodeError:
+                    except TypeError:
                         final_answer = f"{scratchpad.action.action_input}"
                 else:
                     function_call_state = True
diff --git a/api/core/agent/fc_agent_runner.py b/api/core/agent/fc_agent_runner.py
index 4e6fe60e57..9eb853aa74 100644
--- a/api/core/agent/fc_agent_runner.py
+++ b/api/core/agent/fc_agent_runner.py
@@ -126,8 +126,8 @@ class FunctionCallAgentRunner(BaseAgentRunner):
                             tool_call_inputs = json.dumps(
                                 {tool_call[1]: tool_call[2] for tool_call in tool_calls}, ensure_ascii=False
                             )
-                        except json.JSONDecodeError:
-                            # ensure ascii to avoid encoding error
+                        except TypeError:
+                            # fallback: force ASCII to handle non-serializable objects
                             tool_call_inputs = json.dumps({tool_call[1]: tool_call[2] for tool_call in tool_calls})
 
                     if chunk.delta.message and chunk.delta.message.content:
@@ -153,8 +153,8 @@ class FunctionCallAgentRunner(BaseAgentRunner):
                         tool_call_inputs = json.dumps(
                             {tool_call[1]: tool_call[2] for tool_call in tool_calls}, ensure_ascii=False
                         )
-                    except json.JSONDecodeError:
-                        # ensure ascii to avoid encoding error
+                    except TypeError:
+                        # fallback: force ASCII to handle non-serializable objects
                         tool_call_inputs = json.dumps({tool_call[1]: tool_call[2] for tool_call in tool_calls})
 
                 if result.usage: