diff --git a/gtk/src/gtk_sound_driver_sdl.h b/gtk/src/gtk_sound_driver_sdl.h
index f9115c4f..18083a15 100644
--- a/gtk/src/gtk_sound_driver_sdl.h
+++ b/gtk/src/gtk_sound_driver_sdl.h
@@ -8,6 +8,7 @@
 #define __GTK_SOUND_DRIVER_SDL_H
 
 #include "SDL.h"
+// SDL.h may include altivec.h which redefines vector and bool
 #undef vector
 #undef bool