diff --git a/render/mask.h b/render/mask.h
index 2eed4c07..90a622b3 100644
--- a/render/mask.h
+++ b/render/mask.h
@@ -1,6 +1,8 @@
 #ifndef __mask_h
 #define __mask_h
 
+#include <X11/Xlib.h>
+
 typedef struct {
   Pixmap mask;
   guint w, h;