diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index ac4e03c004..aa4d017187 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -116,6 +116,7 @@
 		<li>[Fix] Topic searches by author no longer return invalid results (Bug #11777)</li>
 		<li>[Change] Don't allow redirects to different domains. (thanks nookieman)</li>
 		<li>[Fix] Delete drafts and bookmarks when deleting an user. (#27585, thanks Schumi for the fix)</li>
+		<li>[Fix] Set last_post_subject for new topics. (#23945)</li>
 	</ul>
 
 	<a name="v300"></a><h3>1.ii. Changes since 3.0.0</h3>
diff --git a/phpBB/includes/functions_posting.php b/phpBB/includes/functions_posting.php
index a7b9cc5bd5..fe41bc448d 100644
--- a/phpBB/includes/functions_posting.php
+++ b/phpBB/includes/functions_posting.php
@@ -1862,6 +1862,7 @@ function submit_post($mode, $subject, $username, $topic_type, &$poll, &$data, $u
 				'topic_last_poster_id'		=> (int) $user->data['user_id'],
 				'topic_last_poster_name'	=> (!$user->data['is_registered'] && $username) ? $username : (($user->data['user_id'] != ANONYMOUS) ? $user->data['username'] : ''),
 				'topic_last_poster_colour'	=> $user->data['user_colour'],
+				'topic_last_post_subject'	=> (string) $subject,
 			);
 		}