Index: lib/redmine/i18n.rb
===================================================================
--- lib/redmine/i18n.rb	(revision 21522)
+++ lib/redmine/i18n.rb	(working copy)
@@ -88,7 +88,8 @@
 
       if Setting.timespan_format == 'minutes'
         h = hours.floor
-        m = ((hours - h) * 60).round
+        _hrs, m = ((hours - h) * 60).round.divmod(60)
+        h += _hrs
         "%d:%02d" % [ h, m ]
       else
         "%.2f" % hours.to_f