diff --git a/sane/scanner.cpp b/sane/scanner.cpp
index 977d893..858db4d 100644
--- a/sane/scanner.cpp
+++ b/sane/scanner.cpp
@@ -3494,7 +3494,7 @@ COM_API_IMPLEMENT(scanner, bool, ui_show_setting(HWND parent, bool with_scan, bo
 	events_.clear();
 	ui_notify = std::function<void(int, void*, int)>();
 
-	if (!IsWindowVisible(parent))
+	if (!IsWindow(parent) || !IsWindowVisible(parent))
 		parent = NULL;
 
 	if (callback::show_setting_ui)
@@ -3592,7 +3592,7 @@ COM_API_IMPLEMENT(scanner, bool, ui_show_progress(HWND parent, bool bIndicator))
 	is_bIndicator = bIndicator;
 	if (is_bIndicator)
 		ui_notify = std::function<void(int, void*, int)>();
-	if (!IsWindowVisible(parent))
+	if (!IsWindow(parent) || !IsWindowVisible(parent))
 		parent = NULL;
 
 	auto ui_process = [this](ui_result res)