diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 7efbbe8..5cfaaa0 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -984,3 +984,19 @@
   call assert_fails("call libcall('Xdoesnotexist_', 'getenv', 'HOME')", 'E364:')
   call assert_fails("call libcallnr('Xdoesnotexist_', 'strlen', 'abcd')", 'E364:')
 endfunc
+
+sandbox function Fsandbox()
+  normal ix
+endfunc
+
+func Test_func_sandbox()
+  sandbox let F = {-> 'hello'}
+  call assert_equal('hello', F())
+
+  sandbox let F = {-> execute("normal ix\<Esc>")}
+  call assert_fails('call F()', 'E48:')
+  unlet F
+
+  call assert_fails('call Fsandbox()', 'E48:')
+  delfunc Fsandbox
+endfunc