Index: public/javascripts/calendar/calendar.js
===================================================================
--- public/javascripts/calendar/calendar.js	(revision 3440)
+++ public/javascripts/calendar/calendar.js	(working copy)
@@ -1698,7 +1698,7 @@
 Date.prototype.getWeekNumber = function() {
 	var d = new Date(this.getFullYear(), this.getMonth(), this.getDate(), 0, 0, 0);
 	var DoW = d.getDay();
-	d.setDate(d.getDate() - (DoW + 6) % 7 + 3); // Nearest Thu
+	d.setDate(d.getDate() - DoW % 7 + 4); // This weeks Thu
 	var ms = d.valueOf(); // GMT
 	d.setMonth(0);
 	d.setDate(4); // Thu in Week 1