diff --git a/src/slic3r/GUI/GUI_Preview.cpp b/src/slic3r/GUI/GUI_Preview.cpp
index 0d6fdeb8d9..50e48c965c 100644
--- a/src/slic3r/GUI/GUI_Preview.cpp
+++ b/src/slic3r/GUI/GUI_Preview.cpp
@@ -21,6 +21,7 @@
 #include "DoubleSliderForLayers.hpp"
 #include "ExtruderSequenceDialog.hpp"
 #include "Plater.hpp"
+#include "Tab.hpp"
 #include "MainFrame.hpp"
 #include "MsgDialog.hpp"
 #include "format.hpp"
@@ -456,7 +457,7 @@ void Preview::create_sliders()
                     return "";
 
                 value = into_u8(dlg.GetValue());
-                valid = true;// GUI::Tab::validate_custom_gcode("Custom G-code", value); // !ysFIXME validate_custom_gcode
+                valid = Tab::validate_custom_gcode("Custom G-code", value);
             } while (!valid);
             return value;
         });