diff --git a/Gemfile b/Gemfile
index ea4ee913..45ec242d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,6 +15,7 @@ gem 'jquery-rails', '2.1.4'
 gem 'jquery-ui-rails'
 gem "select2-rails", '3.3.1'
 gem 'kaminari'
+gem 'time_difference'
 
 # gem "memcached", "~> 1.4.3"
 # gem "memcache-client"