diff --git a/lib/vagrant-hostmanager/hosts_file.rb b/lib/vagrant-hostmanager/hosts_file.rb
index d7a2e58..71b4e05 100644
--- a/lib/vagrant-hostmanager/hosts_file.rb
+++ b/lib/vagrant-hostmanager/hosts_file.rb
@@ -129,8 +129,10 @@ module VagrantPlugins
 
       ## Windows support for copying files, requesting elevated privileges if necessary
       module WindowsSupport
+        require 'rbconfig'
+
         def self.windows?
-          ENV['OS'] === 'Windows_NT'
+          RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/
         end
 
         require 'win32ole' if windows?