diff --git a/lib/devise.rb b/lib/devise.rb
index c064b223..713c5c7e 100644
--- a/lib/devise.rb
+++ b/lib/devise.rb
@@ -199,6 +199,11 @@ module Devise
   # to provide custom routes.
   mattr_accessor :router_name
   @@router_name = nil
+  
+  # Set the omniauth path prefix so it can be overriden when
+  # Devise is used in a mountable engine
+  mattr_accessor :omniauth_path_prefix
+  @@omniauth_path_prefix = nil
 
   def self.encryptor=(value)
     warn "\n[DEVISE] To select a encryption which isn't bcrypt, you should use devise-encryptable gem.\n"
diff --git a/lib/devise/rails/routes.rb b/lib/devise/rails/routes.rb
index 9eada5a4..0125a1ec 100644
--- a/lib/devise/rails/routes.rb
+++ b/lib/devise/rails/routes.rb
@@ -382,7 +382,7 @@ module ActionDispatch::Routing
 
       def devise_omniauth_callback(mapping, controllers) #:nodoc:
         path, @scope[:path] = @scope[:path], nil
-        path_prefix = "/#{mapping.path}/auth".squeeze("/")
+        path_prefix = Devise.omniauth_path_prefix || "/#{mapping.path}/auth".squeeze("/")
         set_omniauth_path_prefix!(path_prefix)
 
         match "#{path_prefix}/:action/callback", :constraints => { :action => Regexp.union(mapping.to.omniauth_providers.map(&:to_s)) },