diff --git a/lib/nerdtree/ui.vim b/lib/nerdtree/ui.vim
index fc9db71..9ffadf6 100644
--- a/lib/nerdtree/ui.vim
+++ b/lib/nerdtree/ui.vim
@@ -284,7 +284,11 @@ endfunction
 function! s:UI._indentLevelFor(line)
     " Replace multi-character DirArrows with a single space so the
     " indentation calculation doesn't get messed up.
-    let l:line = substitute(substitute(a:line, '\V'.g:NERDTreeDirArrowExpandable, ' ', ''), '\V'.g:NERDTreeDirArrowCollapsible, ' ', '')
+    if g:NERDTreeDirArrowExpandable ==# ''
+        let l:line = '  '.a:line
+    else
+        let l:line = substitute(substitute(a:line, '\V'.g:NERDTreeDirArrowExpandable, ' ', ''), '\V'.g:NERDTreeDirArrowCollapsible, ' ', '')
+    endif
     let leadChars = match(l:line, '\M\[^ ]')
     return leadChars / s:UI.IndentWid()
 endfunction