diff --git a/src/video/x11/SDL_x11messagebox.c b/src/video/x11/SDL_x11messagebox.c
index ab2174e02a..cbc3c98c18 100644
--- a/src/video/x11/SDL_x11messagebox.c
+++ b/src/video/x11/SDL_x11messagebox.c
@@ -30,7 +30,10 @@
 #include <X11/keysym.h>
 #include <locale.h>
 
+#ifndef SDL_FORK_MESSAGEBOX
 #define SDL_FORK_MESSAGEBOX 1
+#endif
+
 #define SDL_SET_LOCALE      1
 
 #if SDL_FORK_MESSAGEBOX