diff --git a/inc/config.php b/inc/config.php
index 0cece593..dae61ce6 100644
--- a/inc/config.php
+++ b/inc/config.php
@@ -976,11 +976,11 @@
 
 	// Timezone to use for displaying dates/times.
 	$config['timezone'] = 'America/Los_Angeles';
-	// The format string passed to strftime() for displaying dates.
-	// http://www.php.net/manual/en/function.strftime.php
-	$config['post_date'] = '%m/%d/%y (%a) %H:%M:%S';
+	// The format string passed to date_format() for displaying dates. ISO 8601-like by default.
+	// https://www.php.net/manual/en/datetime.format.php
+	$config['post_date'] = 'd-m-Y (D) H:i:s';
 	// Same as above, but used for "you are banned' pages.
-	$config['ban_date'] = '%A %e %B, %Y';
+	$config['ban_date'] = 'l j F, Y';
 
 	// The names on the post buttons. (On most imageboards, these are both just "Post").
 	$config['button_newtopic'] = _('New Topic');
diff --git a/inc/template.php b/inc/template.php
index fb75aaf6..12d398d7 100644
--- a/inc/template.php
+++ b/inc/template.php
@@ -113,7 +113,6 @@ class Tinyboard extends Twig\Extension\AbstractExtension
 		return array(
 			new Twig\TwigFunction('time', 'time'),
 			new Twig\TwigFunction('floor', 'floor'),
-			new Twig\TwigFunction('timezone', 'twig_timezone_function'),
 			new Twig\TwigFunction('hiddenInputs', 'hiddenInputs'),
 			new Twig\TwigFunction('hiddenInputsHash', 'hiddenInputsHash'),
 			new Twig\TwigFunction('ratio', 'twig_ratio_function'),
@@ -134,17 +133,14 @@ class Tinyboard extends Twig\Extension\AbstractExtension
 	}
 }
 
-function twig_timezone_function() {
-	return 'Z';
-}
-
 function twig_push_filter($array, $value) {
 	array_push($array, $value);
 	return $array;
 }
 
 function twig_date_filter($date, $format) {
-	return gmstrftime($format, $date);
+	$date = new DateTime($date, new DateTimeZone('UTC'));
+	return $date->format($format);
 }
 
 function twig_hasPermission_filter($mod, $permission, $board = null) {
diff --git a/templates/post/time.html b/templates/post/time.html
index e6273f94..518a34b6 100644
--- a/templates/post/time.html
+++ b/templates/post/time.html
@@ -1 +1 @@
- <time datetime="{{ post.time|date('%Y-%m-%dT%H:%M:%S') }}{{ timezone() }}">{{ post.time|date(config.post_date) }}</time>
+ <time datetime="{{ post.time|date('Y-m-d\\TH:i:s\Z') }}">{{ post.time|date(config.post_date) }}</time>
diff --git a/templates/themes/basic/index.html b/templates/themes/basic/index.html
index 98cd0e39..02bc4387 100644
--- a/templates/themes/basic/index.html
+++ b/templates/themes/basic/index.html
@@ -29,7 +29,7 @@
 					{% else %}
 						<em>no subject</em>
 					{% endif %}
-					<span class="unimportant"> &mdash; by {{ entry.name }} at {{ entry.time|date(config.post_date, config.timezone) }}</span>
+					<span class="unimportant"> &mdash; by {{ entry.name }} at {{ entry.time|date(config.post_date) }}</span>
 				</h2>
 				<p>{{ entry.body }}</p>
 			{% endfor %}
diff --git a/templates/themes/catalog/catalog.html b/templates/themes/catalog/catalog.html
index de7d1461..fefaec54 100644
--- a/templates/themes/catalog/catalog.html
+++ b/templates/themes/catalog/catalog.html
@@ -51,7 +51,7 @@
 						{% else %}
 							<img src="{{post.file}}"
 						{% endif %}
-						 id="img-{{ post.id }}" data-subject="{% if post.subject %}{{ post.subject|e }}{% endif %}" data-name="{{ post.name|e }}" data-muhdifference="{{ post.muhdifference }}" class="{{post.board}} thread-image" title="{{post.bump|date('%b %d %H:%M')}}">
+						 id="img-{{ post.id }}" data-subject="{% if post.subject %}{{ post.subject|e }}{% endif %}" data-name="{{ post.name|e }}" data-muhdifference="{{ post.muhdifference }}" class="{{post.board}} thread-image" title="{{post.bump|date('M d H:i')}}">
 					</a>
 						<div class="replies">
 							<strong>R: {{ post.reply_count }} / I: {{ post.image_count }}{% if post.sticky %} (sticky){% endif %}</strong>
diff --git a/templates/themes/sitemap/sitemap.xml b/templates/themes/sitemap/sitemap.xml
index 30033239..8c4a9fa2 100644
--- a/templates/themes/sitemap/sitemap.xml
+++ b/templates/themes/sitemap/sitemap.xml
@@ -10,7 +10,7 @@
 		{% for thread in thread_list %}
 			<url>
 				<loc>{{ settings.url ~ (config.board_path | format(board)) ~ config.dir.res ~ link_for(thread) }}</loc>
-				<lastmod>{{ thread.lastmod | date('%Y-%m-%dT%H:%M:%S') }}{{ timezone() }}</lastmod>
+				<lastmod>{{ thread.lastmod | date('Y-m-d\\TH:i:s\Z') }}</lastmod>
 				<changefreq>{{ settings.changefreq }}</changefreq>
 			</url>
 		{% endfor %}