diff --git a/autoload/gitgutter/highlight.vim b/autoload/gitgutter/highlight.vim
index e976d59..fb1dba5 100644
--- a/autoload/gitgutter/highlight.vim
+++ b/autoload/gitgutter/highlight.vim
@@ -133,7 +133,7 @@ endfunction
 
 function! s:get_hl(group, what, mode) abort
   let r = synIDattr(synIDtrans(hlID(a:group)), a:what, a:mode)
-  if r ==# ''
+  if index(['', '-1'], r) >= 0
     return 'NONE'
   endif
   return r