diff --git a/lib/index.js b/lib/index.js
index d587175..50034f9 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -298,6 +298,7 @@ GitStats.prototype.ansiCalendar = function (data, callback) {
             theme: data.theme
           , start: data.start
           , end: data.end
+          , firstDay: data.firstDay
         }));
     });