diff --git a/autoload/airline/parts.vim b/autoload/airline/parts.vim
index cc003ae0..eab96242 100644
--- a/autoload/airline/parts.vim
+++ b/autoload/airline/parts.vim
@@ -70,8 +70,7 @@ function! airline#parts#iminsert()
 endfunction
 
 function! airline#parts#readonly()
-  let buffer=winbufnr('')
-  if &readonly && &modifiable && !filereadable(buffer)
+  if &readonly && &modifiable && !filereadable(bufname('%'))
     return '[noperm]'
   else
     return &readonly ? g:airline_symbols.readonly : ''