diff --git a/lib/mongoid_search/mongoid_search.rb b/lib/mongoid_search/mongoid_search.rb
index 4309e06..886c0de 100644
--- a/lib/mongoid_search/mongoid_search.rb
+++ b/lib/mongoid_search/mongoid_search.rb
@@ -17,7 +17,7 @@ def search_in(*args)
       self.search_fields      = (self.search_fields || []).concat args
 
       field :_keywords, :type => Array
-      index :_keywords, background: true
+      index :_keywords, :background => true
 
       before_save :set_keywords
     end