diff --git a/usr.bin/make/lst.c b/usr.bin/make/lst.c
index 8f3c32ef72e6..372973112783 100644
--- a/usr.bin/make/lst.c
+++ b/usr.bin/make/lst.c
@@ -1,4 +1,4 @@
-/* $NetBSD: lst.c,v 1.104 2021/02/01 19:39:31 rillig Exp $ */
+/* $NetBSD: lst.c,v 1.105 2021/03/15 16:45:30 rillig Exp $ */
 
 /*
  * Copyright (c) 1988, 1989, 1990, 1993
@@ -34,7 +34,7 @@
 
 #include "make.h"
 
-MAKE_RCSID("$NetBSD: lst.c,v 1.104 2021/02/01 19:39:31 rillig Exp $");
+MAKE_RCSID("$NetBSD: lst.c,v 1.105 2021/03/15 16:45:30 rillig Exp $");
 
 static ListNode *
 LstNodeNew(ListNode *prev, ListNode *next, void *datum)
@@ -205,7 +205,7 @@ Lst_FindDatum(List *list, const void *datum)
 
 /*
  * Move all nodes from src to the end of dst.
- * The source list becomes empty but is not freed.
+ * The source list becomes indeterminate.
  */
 void
 Lst_MoveAll(List *dst, List *src)
@@ -219,6 +219,10 @@ Lst_MoveAll(List *dst, List *src)
 
 		dst->last = src->last;
 	}
+#ifdef CLEANUP
+	src->first = NULL;
+	src->last = NULL;
+#endif
 }
 
 /* Copy the element data from src to the start of dst. */