diff --git a/IkiWiki.pm b/IkiWiki.pm
index 7afd57993..f414996db 100644
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -619,9 +619,20 @@ sub checkconfig () {
 	if (defined $config{timezone} && length $config{timezone}) {
 		$ENV{TZ}=$config{timezone};
 	}
-	else {
+	elsif (defined $ENV{TZ} && length $ENV{TZ}) {
 		$config{timezone}=$ENV{TZ};
 	}
+	else {
+		eval q{use Config qw()};
+		error($@) if $@;
+
+		if ($Config::Config{d_gnulibc} && -e '/etc/localtime') {
+			$config{timezone}=$ENV{TZ}=':/etc/localtime';
+		}
+		else {
+			$config{timezone}=$ENV{TZ}='GMT';
+		}
+	}
 
 	if ($config{w3mmode}) {
 		eval q{use Cwd q{abs_path}};
diff --git a/debian/changelog b/debian/changelog
index fbb5e7f21..8dc5790fc 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -8,6 +8,8 @@ ikiwiki (3.20150108) UNRELEASED; urgency=medium
     bundle an old enough Encode.pm for that not to be a problem: the
     system might have a newer Encode.pm installed separately, like Fedora 20.
     (Closes: #776181; thanks, Anders Kaseorg)
+  * If neither timezone nor TZ is set, set both to :/etc/localtime if
+    we're on a GNU system and that file exists, or GMT otherwise
 
  -- Joey Hess <id@joeyh.name>  Sat, 24 Jan 2015 23:59:20 -0400