diff --git a/routers/static_filter.go b/routers/static_filter.go
index 0d649879..9dbf4d02 100644
--- a/routers/static_filter.go
+++ b/routers/static_filter.go
@@ -77,6 +77,7 @@ func StaticFilter(ctx *context.Context) {
 			panic(err)
 		}
 		dir = strings.ReplaceAll(dir, "\\", "/")
+		ctx.ResponseWriter.WriteHeader(http.StatusNotFound)
 		errorText := fmt.Sprintf("The Casdoor frontend HTML file: \"index.html\" was not found, it should be placed at: \"%s/web/build/index.html\". For more information, see: https://casdoor.org/docs/basic/server-installation/#frontend-1", dir)
 		http.ServeContent(ctx.ResponseWriter, ctx.Request, "Casdoor frontend has encountered error...", time.Now(), strings.NewReader(errorText))
 		return