try to fall back to RAILS_ROOT if Rails.root is not available, before using .

Author: jashkenas

lib/jammit.rb

@@ -8,7 +8,7 @@ module Jammit
 
   ROOT                  = File.expand_path(File.dirname(__FILE__) + '/..')
 
-  ASSET_ROOT            = File.expand_path((defined?(Rails) && Rails.root.to_s.length > 0) ? Rails.root : ".") unless defined?(ASSET_ROOT)
+  ASSET_ROOT            = File.expand_path((defined?(Rails) && Rails.root.to_s.length > 0) ? Rails.root : ENV['RAILS_ROOT'] || ".") unless defined?(ASSET_ROOT)
 
   PUBLIC_ROOT           = (defined?(Rails) && Rails.public_path.to_s.length > 0) ? Rails.public_path : File.join(ASSET_ROOT, 'public') unless defined?(PUBLIC_ROOT)