diff --git a/hgdriver/hgdev/hg_scanner_239.cpp b/hgdriver/hgdev/hg_scanner_239.cpp
index 968bdbf..8329887 100644
--- a/hgdriver/hgdev/hg_scanner_239.cpp
+++ b/hgdriver/hgdev/hg_scanner_239.cpp
@@ -303,8 +303,6 @@ int hg_scanner_239::get_devs_distortion_check_val(float& data)
 }
 int hg_scanner_239::set_auto_flat(int data)
 {
-	std::lock_guard<std::mutex>      lock(io_lock_);
-
 	int ret = SCANNER_ERR_OK;
 	auto fw = get_firmware_version();
 	if (fw.empty())
@@ -321,6 +319,8 @@ int hg_scanner_239::set_auto_flat(int data)
 	}
 	else
 	{
+		std::lock_guard<std::mutex>      lock(io_lock_);
+
 		ret = write_register(setting3399::SC_AUTOCORRECT, data);
 		if (ret != SCANNER_ERR_OK)
 		{