diff --git a/phpBB/includes/ucp/ucp_main.php b/phpBB/includes/ucp/ucp_main.php
index f567c91435..40c866f77c 100644
--- a/phpBB/includes/ucp/ucp_main.php
+++ b/phpBB/includes/ucp/ucp_main.php
@@ -396,23 +396,25 @@ class ucp_main
 						if ($row['forum_last_post_id'])
 						{
 							$last_post_time = $user->format_date($row['forum_last_post_time']);
+							$last_post_time_rfc3339 = gmdate(DATE_RFC3339, $row['forum_last_post_time']);
 							$last_post_url = append_sid("{$phpbb_root_path}viewtopic.$phpEx", "p=" . $row['forum_last_post_id']) . '#p' . $row['forum_last_post_id'];
 						}
 						else
 						{
-							$last_post_time = $last_post_url = '';
+							$last_post_time = $last_post_time_rfc3339 = $last_post_url = '';
 						}
 
 						$template_vars = array(
-							'FORUM_ID'				=> $forum_id,
-							'FORUM_IMG_STYLE'		=> $folder_image,
-							'FORUM_FOLDER_IMG'		=> $user->img($folder_image, $folder_alt),
-							'FORUM_IMAGE'			=> ($row['forum_image']) ? '<img src="' . $phpbb_root_path . $row['forum_image'] . '" alt="' . $user->lang[$folder_alt] . '" />' : '',
-							'FORUM_IMAGE_SRC'		=> ($row['forum_image']) ? $phpbb_root_path . $row['forum_image'] : '',
-							'FORUM_NAME'			=> $row['forum_name'],
-							'FORUM_DESC'			=> generate_text_for_display($row['forum_desc'], $row['forum_desc_uid'], $row['forum_desc_bitfield'], $row['forum_desc_options']),
-							'LAST_POST_SUBJECT'		=> $row['forum_last_post_subject'],
-							'LAST_POST_TIME'		=> $last_post_time,
+							'FORUM_ID'					=> $forum_id,
+							'FORUM_IMG_STYLE'			=> $folder_image,
+							'FORUM_FOLDER_IMG'			=> $user->img($folder_image, $folder_alt),
+							'FORUM_IMAGE'				=> ($row['forum_image']) ? '<img src="' . $phpbb_root_path . $row['forum_image'] . '" alt="' . $user->lang[$folder_alt] . '" />' : '',
+							'FORUM_IMAGE_SRC'			=> ($row['forum_image']) ? $phpbb_root_path . $row['forum_image'] : '',
+							'FORUM_NAME'				=> $row['forum_name'],
+							'FORUM_DESC'				=> generate_text_for_display($row['forum_desc'], $row['forum_desc_uid'], $row['forum_desc_bitfield'], $row['forum_desc_options']),
+							'LAST_POST_SUBJECT'			=> $row['forum_last_post_subject'],
+							'LAST_POST_TIME'			=> $last_post_time,
+							'LAST_POST_TIME_RFC3339'	=> $last_post_time_rfc3339,
 
 							'LAST_POST_AUTHOR'			=> get_username_string('username', $row['forum_last_poster_id'], $row['forum_last_poster_name'], $row['forum_last_poster_colour']),
 							'LAST_POST_AUTHOR_COLOUR'	=> get_username_string('colour', $row['forum_last_poster_id'], $row['forum_last_poster_name'], $row['forum_last_poster_colour']),
diff --git a/phpBB/styles/prosilver/template/forumlist_body.html b/phpBB/styles/prosilver/template/forumlist_body.html
index 099b5f8e3a..7c17e05d0d 100644
--- a/phpBB/styles/prosilver/template/forumlist_body.html
+++ b/phpBB/styles/prosilver/template/forumlist_body.html
@@ -104,7 +104,7 @@
 									{{ Icon('iconify', 'mdi:alert-decagram', lang('POSTS_UNAPPROVED_FORUM'), true, 'c-unapproved-icon') }}
 								</a>
 							<!-- ENDIF -->
-							<!-- IF forumrow.LAST_POST_TIME -->
+							<!-- IF forumrow.LAST_POST_TIME_RFC3339 -->
 								<dfn>{L_LAST_POST}</dfn>
 								<!-- IF forumrow.S_DISPLAY_SUBJECT -->
 									<!-- EVENT forumlist_body_last_post_title_prepend -->
diff --git a/phpBB/styles/prosilver/template/ucp_main_subscribed.html b/phpBB/styles/prosilver/template/ucp_main_subscribed.html
index 8a4a926c89..f72869b108 100644
--- a/phpBB/styles/prosilver/template/ucp_main_subscribed.html
+++ b/phpBB/styles/prosilver/template/ucp_main_subscribed.html
@@ -43,12 +43,12 @@
 					</div>
 				</dt>
 				<dd class="lastpost">
-					<!-- IF forumrow.LAST_POST_TIME -->
+					<!-- IF forumrow.LAST_POST_TIME_RFC3339 -->
 						<span><dfn>{L_LAST_POST} </dfn>{L_POST_BY_AUTHOR} {forumrow.LAST_POST_AUTHOR_FULL}
 							<a href="{forumrow.U_LAST_POST}">
 								{{ Icon('iconify', 'fa:external-link-square', VIEW_LATEST_POST, true, 'c-last-post-icon') }}
 							</a>
-							<br />{forumrow.LAST_POST_TIME}</span>
+							<br /><time datetime="{forumrow.LAST_POST_TIME_RFC3339}">{forumrow.LAST_POST_TIME}</time></span>
 					<!-- ELSE -->
 						{L_NO_POSTS}<br />&nbsp;
 					<!-- ENDIF -->