diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index c5f56c2..1d62ac1 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -847,6 +847,9 @@
   assert_equal(['sdf', 'asdf', 'end'], list3)
 
   v9.CheckDefExecFailure(['var ll = [1, 2, 3]', 'll[-4] = 6'], 'E684:')
+  v9.CheckDefExecFailure(['var ll = [1, 2, 3]', 'unlet ll[8 : 9]'], 'E684:')
+  v9.CheckDefExecFailure(['var ll = [1, 2, 3]', 'unlet ll[1 : -9]'], 'E684:')
+  v9.CheckDefExecFailure(['var ll = [1, 2, 3]', 'unlet ll[2 : 1]'], 'E684:')
 
   # type becomes list<any>
   var somelist = rand() > 0 ? [1, 2, 3] : ['a', 'b', 'c']
@@ -2193,6 +2196,10 @@
     'g:dd = {"a": 1, 2: 2}'
     'unlet g:dd[0z11]',
     ], 'E1029:', 2)
+  v9.CheckDefExecFailure([
+    'g:str = "a string"'
+    'unlet g:str[0]',
+    ], 'E1148: Cannot index a string', 2)
 
   # can compile unlet before variable exists
   g:someDict = {key: 'val'}