diff --git a/src/testdir/test_expand_dllpath.vim b/src/testdir/test_expand_dllpath.vim
index d8ab416..b3e099a 100644
--- a/src/testdir/test_expand_dllpath.vim
+++ b/src/testdir/test_expand_dllpath.vim
@@ -14,7 +14,7 @@
 endfunc
 
 func s:generate_test_if_exists(optname)
-  if exists('&' . a:optname)
+  if exists('+' . a:optname)
     execute join([
           \ 'func Test_expand_' . a:optname . '()',
           \ '  call s:test_expand_dllpath("' . a:optname . '")',