diff --git a/GUI/mainwindow/ISingleton.h b/GUI/Models/ISingleton.h
similarity index 84%
rename from GUI/mainwindow/ISingleton.h
rename to GUI/Models/ISingleton.h
index a6fc5116aaa1da393d8c3d20bdc1f996073e5dac..0865afdc47ecf4b20fbacc5640813ac838d40a6e 100644
--- a/GUI/mainwindow/ISingleton.h
+++ b/GUI/Models/ISingleton.h
@@ -2,7 +2,7 @@
 //
 //  BornAgain: simulate and fit reflection and scattering
 //
-//! @file      GUI/mainwindow/ISingleton.h
+//! @file      GUI/Models/ISingleton.h
 //! @brief     Defines the standard mix-in ISingleton.
 //!
 //! @homepage  http://www.bornagainproject.org
@@ -12,8 +12,8 @@
 //
 //  ************************************************************************************************
 
-#ifndef BORNAGAIN_GUI_MAINWINDOW_ISINGLETON_H
-#define BORNAGAIN_GUI_MAINWINDOW_ISINGLETON_H
+#ifndef BORNAGAIN_GUI_MODELS_ISINGLETON_H
+#define BORNAGAIN_GUI_MODELS_ISINGLETON_H
 
 //! Base class for singletons.
 //! @ingroup tools_internal
@@ -36,4 +36,4 @@ protected:
     ~ISingleton() = default;
 };
 
-#endif // BORNAGAIN_GUI_MAINWINDOW_ISINGLETON_H
+#endif // BORNAGAIN_GUI_MODELS_ISINGLETON_H
diff --git a/GUI/mainwindow/AppSvc.h b/GUI/mainwindow/AppSvc.h
index 3e331c040900f816fdb123bf190d9d15e977a3c7..b03e0b199b5f9db322730e1367c34423fa1e41ef 100644
--- a/GUI/mainwindow/AppSvc.h
+++ b/GUI/mainwindow/AppSvc.h
@@ -15,7 +15,7 @@
 #ifndef BORNAGAIN_GUI_MAINWINDOW_APPSVC_H
 #define BORNAGAIN_GUI_MAINWINDOW_APPSVC_H
 
-#include "GUI/mainwindow/ISingleton.h"
+#include "GUI/Models/ISingleton.h"
 
 class ProjectManager;
 class MaterialModel;