diff --git a/include/wlr/types/wlr_output_layout.h b/include/wlr/types/wlr_output_layout.h
index 3c150fc0..91456bc0 100644
--- a/include/wlr/types/wlr_output_layout.h
+++ b/include/wlr/types/wlr_output_layout.h
@@ -17,6 +17,8 @@ struct wlr_output_layout {
 		struct wl_signal change;
 		struct wl_signal destroy;
 	} events;
+
+	void *data;
 };
 
 struct wlr_output_layout_output_state;