diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 329591239782d..c27237631dfae 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -65,6 +65,10 @@ func Test_highlight_completion()
   hi Aardig ctermfg=green
   call feedkeys(":hi \<Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"hi Aardig', getreg(':'))
+  call feedkeys(":hi default \<Tab>\<Home>\"\<CR>", 'xt')
+  call assert_equal('"hi default Aardig', getreg(':'))
+  call feedkeys(":hi clear Aa\<Tab>\<Home>\"\<CR>", 'xt')
+  call assert_equal('"hi clear Aardig', getreg(':'))
   call feedkeys(":hi li\<S-Tab>\<Home>\"\<CR>", 'xt')
   call assert_equal('"hi link', getreg(':'))
   call feedkeys(":hi d\<S-Tab>\<Home>\"\<CR>", 'xt')
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index d4bb25e69e4d3..8d4be00d38d2f 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -304,12 +304,18 @@ func Test_syntax_arg_skipped()
   syn clear
 endfunc
 
-func Test_invalid_arg()
+func Test_syntax_invalid_arg()
   call assert_fails('syntax case asdf', 'E390:')
   if has('conceal')
     call assert_fails('syntax conceal asdf', 'E390:')
   endif
   call assert_fails('syntax spell asdf', 'E390:')
+  call assert_fails('syntax clear @ABCD', 'E391:')
+  call assert_fails('syntax include @Xxx', 'E397:')
+  call assert_fails('syntax region X start="{"', 'E399:')
+  call assert_fails('syntax sync x', 'E404:')
+  call assert_fails('syntax keyword Abc a[', 'E789:')
+  call assert_fails('syntax keyword Abc a[bc]d', 'E890:')
 endfunc
 
 func Test_syn_sync()
@@ -378,3 +384,20 @@ func Test_ownsyntax_completion()
   call feedkeys(":ownsyntax java\<C-A>\<C-B>\"\<CR>", 'tx')
   call assert_equal('"ownsyntax java javacc javascript', @:)
 endfunc
+
+func Test_highlight_invalid_arg()
+  if has('gui_running')
+    call assert_fails('hi XXX guifg=xxx', 'E254:')
+  endif
+  call assert_fails('hi DoesNotExist', 'E411:')
+  call assert_fails('hi link', 'E412:')
+  call assert_fails('hi link a', 'E412:')
+  call assert_fails('hi link a b c', 'E413:')
+  call assert_fails('hi XXX =', 'E415:')
+  call assert_fails('hi XXX cterm', 'E416:')
+  call assert_fails('hi XXX cterm=', 'E417:')
+  call assert_fails('hi XXX cterm=DoesNotExist', 'E418:')
+  call assert_fails('hi XXX ctermfg=DoesNotExist', 'E421:')
+  call assert_fails('hi XXX xxx=White', 'E423:')
+endfunc
+