diff --git a/src/video/x11/SDL_x11messagebox.c b/src/video/x11/SDL_x11messagebox.c
index 2d34e9e21..7c3aaec92 100644
--- a/src/video/x11/SDL_x11messagebox.c
+++ b/src/video/x11/SDL_x11messagebox.c
@@ -28,6 +28,7 @@
 #include "SDL_x11dyn.h"
 #include "SDL_assert.h"
 
+#include <X11/keysym.h>
 #include <locale.h>