diff --git a/libguile/list.c b/libguile/list.c
index 07a0d0dc3..74bb2cc3e 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -231,6 +231,7 @@ SCM_DEFINE (scm_append, "append", 0, 0, 1,
     SCM res = SCM_EOL;
     SCM *lloc = &res;
     SCM arg = SCM_CAR (args);
+    int argnum = 1;
     args = SCM_CDR (args);
     while (!SCM_NULLP (args)) {
       while (SCM_CONSP (arg)) {
@@ -238,9 +239,10 @@ SCM_DEFINE (scm_append, "append", 0, 0, 1,
 	lloc = SCM_CDRLOC (*lloc);
 	arg = SCM_CDR (arg);
       }
-      SCM_VALIDATE_NULL_OR_NIL (SCM_ARGn, arg);
+      SCM_VALIDATE_NULL_OR_NIL (argnum, arg);
       arg = SCM_CAR (args);
       args = SCM_CDR (args);
+      argnum++;
     };
     *lloc = arg;
     return res;