diff --git a/src/vim9execute.c b/src/vim9execute.c
index fdca977..9fc942d 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -3677,7 +3677,14 @@
 
 		    // add two lists or blobs
 		    if (iptr->isn_type == ISN_ADDLIST)
-			eval_addlist(tv1, tv2);
+		    {
+			if (iptr->isn_arg.op.op_type == EXPR_APPEND
+						   && tv1->vval.v_list != NULL)
+			    list_extend(tv1->vval.v_list, tv2->vval.v_list,
+									 NULL);
+			else
+			    eval_addlist(tv1, tv2);
+		    }
 		    else
 			eval_addblob(tv1, tv2);
 		    clear_tv(tv2);