diff --git a/tests/core.scm b/tests/core.scm
index a395a075c..58e5650aa 100644
--- a/tests/core.scm
+++ b/tests/core.scm
@@ -705,6 +705,15 @@
         (t.is (iterator->array (gen 100 1 2 3 4 5))
               #(1 2 3 4 5))))
 
+(test.failing "core: append!"
+      (lambda (t)
+        (let ((x ()))
+          (append! x (list 10) (list 20))
+          (t.is x '(10 20)))
+        (let ((x '(1 2)))
+          (append! x (list 3 4))
+          (t.is x '(1 2 3 4)))))
+
 ;; TODO
 ;; begin*
 ;; set-obj! throws with null or boolean