diff -ur joda-time-1.5.1-src.old/src/test/org/joda/time/convert/MockUnknownCalendar.java joda-time-1.5.1-src/src/test/org/joda/time/convert/MockUnknownCalendar.java
--- joda-time-1.5.1-src.old/src/test/org/joda/time/convert/MockUnknownCalendar.java	2007-12-21 00:43:52.000000000 +0200
+++ joda-time-1.5.1-src/src/test/org/joda/time/convert/MockUnknownCalendar.java	2007-12-21 00:46:42.000000000 +0200
@@ -34,7 +34,10 @@
     MockUnknownCalendar(TimeZone zone) {
         this.zone = zone;
     }
-    
+
+    public int compareTo(Object o) {
+        return super.compareTo((Calendar) o);
+    }
     public long getTimeInMillis() {
         return millis;
     }