diff --git a/api/core/llm_generator/output_parser/structured_output.py b/api/core/llm_generator/output_parser/structured_output.py
index 2625aa2d48..6246a9ce8e 100644
--- a/api/core/llm_generator/output_parser/structured_output.py
+++ b/api/core/llm_generator/output_parser/structured_output.py
@@ -143,7 +143,7 @@ def invoke_llm_with_structured_output(
         )
     else:
 
-        def generator():
+        def generator() -> Generator[LLMStructuredOutput, None, None]:
             result_text = ""
             for event in llm_result:
                 if isinstance(event, LLMResultChunk):