diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index e263115..67163e6 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -2062,9 +2062,9 @@
   for in_opt in in_opts
     let x = copy(in_opt)
     for out_opt in out_opts
-      call extend(x, out_opt)
+      let x = extend(copy(x), out_opt)
       for err_opt in err_opts
-        call extend(x, err_opt)
+        let x = extend(copy(x), err_opt)
         let opts += [extend({'pty': 1}, x)]
       endfor
     endfor
diff --git a/src/testdir/test_let.vim b/src/testdir/test_let.vim
index 550655c..40eabb8 100644
--- a/src/testdir/test_let.vim
+++ b/src/testdir/test_let.vim
@@ -142,7 +142,7 @@
   call assert_fails('call s:set_varg4(1)', 'E742:')
   call s:set_varg5([0])
   call assert_fails('call s:set_varg6(1)', 'E742:')
-  " call assert_fails('call s:set_varg7(1)', 'E46:')
+  call assert_fails('call s:set_varg7(1)', 'E742:')
   call assert_fails('call s:set_varg8(1)', 'E742:')
   call s:set_varg9([0])
 endfunction