diff --git a/src/testdir/test_help.vim b/src/testdir/test_help.vim
index 15cc642..6e32edd 100644
--- a/src/testdir/test_help.vim
+++ b/src/testdir/test_help.vim
@@ -134,4 +134,13 @@
   close
 endfunc
 
+func Test_help_long_argument()
+  try
+    exe 'help \%' .. repeat('0', 1021)
+  catch
+    call assert_match("E149:", v:exception)
+  endtry
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab