diff --git a/src/GUI/misc_ui.hpp b/src/GUI/misc_ui.hpp
index 51a677504..fb3930325 100644
--- a/src/GUI/misc_ui.hpp
+++ b/src/GUI/misc_ui.hpp
@@ -29,8 +29,10 @@ enum class OS { Linux, Mac, Windows } ;
 // constants to reduce the proliferation of macros in the rest of the code
 #ifdef __WIN32
 constexpr OS the_os = OS::Windows;
+constexpr bool wxGTK {false};
 #elif __APPLE__
 constexpr OS the_os = OS::Mac;
+constexpr bool wxGTK {false};
 #elif __linux__
 constexpr OS the_os = OS::Linux;
     #ifdef __WXGTK__