diff --git a/frontend/src/core/threads/hooks.ts b/frontend/src/core/threads/hooks.ts
index d8bc08d3..522f8123 100644
--- a/frontend/src/core/threads/hooks.ts
+++ b/frontend/src/core/threads/hooks.ts
@@ -193,14 +193,17 @@ export function useThreadStream({
       handleStreamStart(meta.thread_id);
       setOnStreamThreadId(meta.thread_id);
     },
-    onLangChainEvent(event) {
-      if (event.event === "on_tool_end") {
-        listeners.current.onToolEnd?.({
-          name: event.name,
-          data: event.data,
-        });
-      }
-    },
+    onLangChainEvent:
+      onToolEnd == null
+        ? undefined
+        : (event) => {
+            if (event.event === "on_tool_end") {
+              listeners.current.onToolEnd?.({
+                name: event.name,
+                data: event.data,
+              });
+            }
+          },
     onUpdateEvent(data) {
       const updates: Array<Partial<AgentThreadState> | null> = Object.values(
         data || {},