diff --git a/src/gui/gui.h b/src/gui/gui.h
index 586842864..d54635fa3 100644
--- a/src/gui/gui.h
+++ b/src/gui/gui.h
@@ -1245,6 +1245,7 @@ struct FurnaceGUISysDef {
   const char* extra;
   String definition;
   std::vector<FurnaceGUISysDefChip> orig;
+  std::vector<FurnaceGUISysDef> subDefs;
   FurnaceGUISysDef(const char* n, std::initializer_list<FurnaceGUISysDefChip> def, const char* e=NULL);
 };