diff --git a/sane/scanner.cpp b/sane/scanner.cpp
index a8081e4..9f5d4cf 100644
--- a/sane/scanner.cpp
+++ b/sane/scanner.cpp
@@ -784,6 +784,7 @@ void scanner::on_ui_event(int uev, void* sender)
 			indicator_.reset();
 
 		is_scanning_ = is_show_setting_;
+		ui_notify = std::function<void(int, void*, int)>();
 	}
 	else if (uev == SANE_EVENT_UI_CLOSE_CANCEL)
 	{
@@ -796,6 +797,7 @@ void scanner::on_ui_event(int uev, void* sender)
 	else if (uev == SANE_EVENT_SCAN_FINISHED)
 	{
 		is_scanning_ = is_show_setting_;
+		ui_notify = std::function<void(int, void*, int)>();
 	}
 
 	int(__stdcall * h)(int, void*) = scanner_ev_handler_;
@@ -1422,7 +1424,7 @@ int scanner::thread_start(void)
 		// display error message on progress UI, may be closed immediately by APP, so we hide progress UI and call message_box ...
 		// 
 #ifdef START_SCAN_IN_THREAD
-		if (callback::show_progress_ui && is_bIndicator)
+		if (callback::show_progress_ui && is_bIndicator && ui_notify)
 		{
 			int ev = SANE_EVENT_WORKING;
 		
@@ -3265,6 +3267,7 @@ COM_API_IMPLEMENT(scanner, void, ui_hide(void))
 	if (callback::close_ui)
 		callback::close_ui(UI_INDICATOR | UI_SETTING | UI_MSG_BOX);
 	is_show_setting_ = false;
+	ui_notify = std::function<void(int, void*, int)>();
 }
 COM_API_IMPLEMENT(scanner, bool, ui_is_ok(void))
 {