diff --git a/src/structs.h b/src/structs.h
index e2f1de9..a35361e 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1464,8 +1464,9 @@
 			// allowed to mask existing functions
 
 // Values for "v_lock".
-#define VAR_LOCKED	1	// locked with lock(), can use unlock()
-#define VAR_FIXED	2	// locked forever
+#define VAR_LOCKED	    1	// locked with lock(), can use unlock()
+#define VAR_FIXED	    2	// locked forever
+#define VAR_ITEMS_LOCKED    4	// items of non-materialized list locked
 
 /*
  * Structure to hold an item of a list: an internal variable without a name.
@@ -1497,7 +1498,8 @@
  */
 struct listvar_S
 {
-    listitem_T	*lv_first;	// first item, NULL if none
+    listitem_T	*lv_first;	// first item, NULL if none, &range_list_item
+				// for a non-materialized list
     listwatch_T	*lv_watch;	// first watcher, NULL if none
     union {
 	struct {	// used for non-materialized range list: