diff --git a/plugin/CSApprox.vim b/plugin/CSApprox.vim
index 177673a..3febedf 100644
--- a/plugin/CSApprox.vim
+++ b/plugin/CSApprox.vim
@@ -154,7 +154,7 @@ function! s:Highlights()
 
   let i = 1
   while 1
-    if synIDtrans(i) == 0
+    if synIDtrans(i) == 0 || !len(synIDattr(synIDtrans(i), "name"))
       break
     endif