diff --git a/src/structs.h b/src/structs.h
index 5787d2b..c664f0e 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2916,6 +2916,7 @@
     colnr_T	w_popup_mincol;	    // close popup if cursor before this col
     colnr_T	w_popup_maxcol;	    // close popup if cursor after this col
     int		w_popup_drag;	    // allow moving the popup with the mouse
+    list_T	*w_popup_mask;	    // list of lists for "mask"
 
 # if defined(FEAT_TIMERS)
     timer_T	*w_popup_timer;	    // timer for closing popup window