diff --git a/lib/tracker/api/formatter/time.rb b/lib/tracker/api/formatter/time.rb
index 455b7dd..d862e73 100644
--- a/lib/tracker/api/formatter/time.rb
+++ b/lib/tracker/api/formatter/time.rb
@@ -1,3 +1,5 @@
+require 'time'
+
 module Tracker # :nodoc:
   module Api # :nodoc:
     class Formatter