diff --git a/src/testdir/test_excmd.vim b/src/testdir/test_excmd.vim
index 150e258..f27b385 100644
--- a/src/testdir/test_excmd.vim
+++ b/src/testdir/test_excmd.vim
@@ -327,6 +327,9 @@
 " Test for the :winsize command
 func Test_winsize_cmd()
   call assert_fails('winsize 1', 'E465:')
+  call assert_fails('winsize 1 x', 'E465:')
+  call assert_fails('win_getid(1)', 'E475: Invalid argument: _getid(1)')
+  " Actually changing the window size would be flaky.
 endfunc
 
 " Test for the :redir command