diff -r cf22ac054c08 CHANGES.txt
--- a/CHANGES.txt	Fri Mar 15 15:19:53 2013 +0530
+++ b/CHANGES.txt	Fri Mar 22 11:31:24 2013 +0100
@@ -37,6 +37,8 @@
   when nuking (anatoly techtonik)
 - demo.py changing hostname in config.ini actually changes the address
   where demo.py listens. (John Rouillard)
+- issue2550802: Fixed date so second fraction can't cause rounding to
+  60.000 when serialising. (Erik Hanspers)
 
 2012-12-21: 1.4.21
 
diff -r cf22ac054c08 roundup/date.py
--- a/roundup/date.py	Fri Mar 15 15:19:53 2013 +0530
+++ b/roundup/date.py	Fri Mar 22 11:31:24 2013 +0100
@@ -274,7 +274,7 @@
                 self.second = _local_to_utc(y, m, d, H, M, S, offset)
             # we lost the fractional part
             self.second = self.second + frac
-            if str(self.second) == '60.0': self.second = 59.9
+            self.second = min(self.second, 59.999)
         except:
             raise ValueError, 'Unknown spec %r' % (spec,)