diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index d25bb47..72e1274 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1743,6 +1743,21 @@
   CheckDefFailure(['endif'], 'E580:')
   CheckDefFailure(['if g:abool', 'elseif xxx'], 'E1001:')
   CheckDefFailure(['if true', 'echo 1'], 'E171:')
+
+  var lines =<< trim END
+      var s = ''
+      if s = ''
+      endif
+  END
+  CheckDefFailure(lines, 'E488:')
+
+  lines =<< trim END
+      var s = ''
+      if s == ''
+      elseif s = ''
+      endif
+  END
+  CheckDefFailure(lines, 'E488:')
 enddef
 
 let g:bool_true = v:true
@@ -2200,6 +2215,13 @@
   CheckDefFailure(['break'], 'E587:')
   CheckDefFailure(['if true', 'break'], 'E587:')
   CheckDefFailure(['while 1', 'echo 3'], 'E170:')
+
+  var lines =<< trim END
+      var s = ''
+      while s = ''
+      endwhile
+  END
+  CheckDefFailure(lines, 'E488:')
 enddef
 
 def Test_interrupt_loop()