diff --git a/plugins/providers/virtualbox/synced_folder.rb b/plugins/providers/virtualbox/synced_folder.rb
index <HASH>..<HASH> 100644
--- a/plugins/providers/virtualbox/synced_folder.rb
+++ b/plugins/providers/virtualbox/synced_folder.rb
@@ -85,7 +85,7 @@ module VagrantPlugins
       end
 
       def os_friendly_id(id)
-        id.gsub(/[\/]/,'_').sub(/^_/, '')
+        id.gsub(/[\/\\]/,'_').sub(/^_/, '')
       end
 
       # share_folders sets up the shared folder definitions on the
Escape backward slashes in vbox share name

That fixes invalid share names in Windows guests, where backward slash character is
used as a path separator.