diff --git a/lib/vagrant/action/builtin/box_add.rb b/lib/vagrant/action/builtin/box_add.rb
index 6537937da..fbc6bd51f 100644
--- a/lib/vagrant/action/builtin/box_add.rb
+++ b/lib/vagrant/action/builtin/box_add.rb
@@ -382,6 +382,7 @@ module Vagrant
             file_path = File.expand_path(url)
             file_path = Util::Platform.cygwin_windows_path(file_path)
             file_path = file_path.gsub("\\", "/")
+            file_path = "/#{file_path}" if !file_path.start_with?("/")
             url = "file://#{file_path}"
           end