diff --git a/api/controllers/web/completion.py b/api/controllers/web/completion.py
index 2bb7db015ad..7871b411c4b 100644
--- a/api/controllers/web/completion.py
+++ b/api/controllers/web/completion.py
@@ -32,6 +32,7 @@ from libs.helper import uuid_value
 from models.model import App, AppMode, EndUser
 from services.app_generate_service import AppGenerateService
 from services.app_task_service import AppTaskService
+from services.conversation_service import ConversationService
 from services.errors.llm import InvokeRateLimitError
 
 logger = logging.getLogger(__name__)
@@ -202,6 +203,12 @@ class ChatApi(WebApiResource):
         args["auto_generate_name"] = False
 
         try:
+            # Eagerly validate conversation to avoid hanging on invalid conversation_id
+            if payload.conversation_id:
+                ConversationService.get_conversation(
+                    app_model=app_model, conversation_id=payload.conversation_id, user=end_user
+                )
+
             response = AppGenerateService.generate(
                 app_model=app_model, user=end_user, args=args, invoke_from=InvokeFrom.WEB_APP, streaming=streaming
             )