diff --git a/src/dispextern.h b/src/dispextern.h
index fad5bfd..13ca68c 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2533,6 +2533,7 @@ struct it
   /* If what == IT_XWIDGET.  */
   struct xwidget *xwidget;
 #endif
+  void *foo;
 
   /* Values from `slice' property.  */
   struct it_slice slice;