diff --git a/autoload/nerdtree/ui_glue.vim b/autoload/nerdtree/ui_glue.vim
index b0cedee..aabd2ee 100644
--- a/autoload/nerdtree/ui_glue.vim
+++ b/autoload/nerdtree/ui_glue.vim
@@ -112,6 +112,7 @@ endfunction
 function! s:initCustomOpenArgs() abort
     let l:defaultOpenArgs = {'file': {'reuse': 'all', 'where': 'p'}, 'dir': {}}
     let l:customOpenArgs = get(g:, 'NERDTreeCustomOpenArgs', {})
+    return extend(l:customOpenArgs, l:defaultOpenArgs, 'keep')
 
     if v:false is# s:validateType(l:customOpenArgs, v:t_dict)
         return l:defaultOpenArgs