diff --git a/IkiWiki/Plugin/calendar.pm b/IkiWiki/Plugin/calendar.pm
index cbbb57e98..77fd50827 100644
--- a/IkiWiki/Plugin/calendar.pm
+++ b/IkiWiki/Plugin/calendar.pm
@@ -396,8 +396,14 @@ sub preprocess (@) {
 	}
 	elsif ($params{type} eq 'year' && $params{year} == $thisyear) {
 		# calendar for current year, updates 1st of next month
-		$pagestate{$params{destpage}}{calendar}{nextchange}=
-			timelocal(0, 0, 0, 1, $thismonth+1-1, $params{year});
+		if ($thismonth < 12) {
+			$pagestate{$params{destpage}}{calendar}{nextchange}=
+				timelocal(0, 0, 0, 1, $thismonth+1-1, $params{year});
+		}
+		else {
+			$pagestate{$params{destpage}}{calendar}{nextchange}=
+				timelocal(0, 0, 0, 1, 1-1, $params{year}+1);
+		}
 	}
 	elsif ($params{type} eq 'year' && $params{year} > $thisyear) {
 		# calendar for upcoming year, updates 1st of that year
diff --git a/debian/changelog b/debian/changelog
index 2b468ca2f..3afe89b59 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -14,6 +14,7 @@ ikiwiki (3.20091114) UNRELEASED; urgency=low
     modification date display, etc.
   * htmllink: Allow a title attribute to be specified.
   * calendar: Add title attributes for all links in the calendars.
+  * calendar: Fix month wraparound error that broke in December.
 
  -- Joey Hess <joeyh@debian.org>  Mon, 16 Nov 2009 15:46:45 -0500