diff --git a/sane/DlgPage.cpp b/sane/DlgPage.cpp
index 06cca17..b0b6895 100644
--- a/sane/DlgPage.cpp
+++ b/sane/DlgPage.cpp
@@ -1038,7 +1038,7 @@ void dlg_page::set_ctrl_value(HWND ctrl, SANE_Value_Type type, void* val, bool o
 		{
 			if (type == SANE_TYPE_BOOL)
 			{
-				DWORD	id = GetWindowLong(ctrl, GWL_ID);
+				DWORD	id = GetWindowLong(ctrl, GWL_ID) - dlg_page::dyn_id_base;
 				HWND	host = (HWND)GetPropW(ctrl, dlg_page::property_host.c_str());
 
 				if (IsWindow(host) && (id == id_custom_area_ || id == id_custom_gamma_))