diff --git a/autoload/fugitive.vim b/autoload/fugitive.vim
index 3b3d6a2..d6902a1 100644
--- a/autoload/fugitive.vim
+++ b/autoload/fugitive.vim
@@ -2206,7 +2206,7 @@ function! s:DirArg(path) abort
   if path =~# '^/\|^\a\+:\|^\.\.\=\%(/\|$\)'
     return path
   else
-    return (empty(s:Tree()) ? s:Dir() : s:Tree()) . '/' . path
+    return s:PlatformSlash((empty(s:Tree()) ? s:Dir() : s:Tree()) . '/' . path)
   endif
 endfunction