diff --git a/src/testdir/test_assign.vim b/src/testdir/test_assign.vim
index 317d458..1715a3f 100644
--- a/src/testdir/test_assign.vim
+++ b/src/testdir/test_assign.vim
@@ -23,11 +23,11 @@
     let &t_k1 = old_t_k1
   endif
 
-  call assert_fails('let x = &t_xx', 'E15')
+  call assert_fails('let x = &t_xx', 'E113')
   let &t_xx = "yes"
   call assert_equal("yes", &t_xx)
   let &t_xx = ""
-  call assert_fails('let x = &t_xx', 'E15')
+  call assert_fails('let x = &t_xx', 'E113')
 endfunc
 
 func Test_let_option_error()
@@ -43,3 +43,11 @@
   call assert_equal("vert:|", &fillchars)
   let &fillchars = _w
 endfunc
+
+func Test_let_errors()
+  let s = 'abcd'
+  call assert_fails('let s[1] = 5', 'E689:')
+
+  let l = [1, 2, 3]
+  call assert_fails('let l[:] = 5', 'E709:')
+endfunc