diff --git a/autoload/fugitive.vim b/autoload/fugitive.vim
index a7f008d..3d15275 100644
--- a/autoload/fugitive.vim
+++ b/autoload/fugitive.vim
@@ -275,8 +275,9 @@ endfunction
 
 function! s:Map(mode, lhs, rhs, ...) abort
   let maps = []
-  let defer = a:0 && a:1 =~# '<unique>' || get(g:, 'fugitive_defer_to_existing_maps')
-  let flags = substitute(a:0 ? a:1 : '', '<unique>', '', '') . (a:rhs =~# '<Plug>' ? '' : '<script>') . '<nowait>'
+  let flags = a:0 && type(a:1) == type('') ? a:1 : ''
+  let defer = flags =~# '<unique>'
+  let flags = substitute(flags, '<unique>', '', '') . (a:rhs =~# '<Plug>' ? '' : '<script>') . '<nowait>'
   for mode in split(a:mode, '\zs')
     if a:0 <= 1
       call add(maps, mode.'map <buffer>' . substitute(flags, '<unique>', '', '') . ' <Plug>fugitive:' . a:lhs . ' ' . a:rhs)