diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index d8a5432113..e9f5994a7c 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -135,6 +135,7 @@
 		<li>[Fix] Sort backups by date, newest first (Bug #14818)</li>
 		<li>[Fix] Prevent incomplete backups stored if option &quot;store and download&quot; is selected and admin cancel download by removing the option. (Bug #20325)</li>
 		<li>[Fix] Enforce correct case for template variables</li>
+		<li>[Fix] Set topic_last_view_time on post/reply/edit to circumvent race conditions in auto prune and false removal of topics for manual forum prune (Bug #18055, #43515)</li>
 		<li>[Change] Allow download of conflicting file for later reference in automatic updater</li>
 		<li>[Change] Default difference view is now 'inline' instead of 'side by side'</li>
 		<li>[Change] Added new option for merging differences to conflicting files in automatic updater</li>
diff --git a/phpBB/includes/functions_posting.php b/phpBB/includes/functions_posting.php
index e44454b5ff..9b7f8e001f 100644
--- a/phpBB/includes/functions_posting.php
+++ b/phpBB/includes/functions_posting.php
@@ -1738,6 +1738,7 @@ function submit_post($mode, $subject, $username, $topic_type, &$poll, &$data, $u
 			$sql_data[TOPICS_TABLE]['sql'] = array(
 				'topic_poster'				=> (int) $user->data['user_id'],
 				'topic_time'				=> $current_time,
+				'topic_last_view_time'		=> $current_time,
 				'forum_id'					=> ($topic_type == POST_GLOBAL) ? 0 : $data['forum_id'],
 				'icon_id'					=> $data['icon_id'],
 				'topic_approved'			=> $post_approval,
@@ -1785,7 +1786,13 @@ function submit_post($mode, $subject, $username, $topic_type, &$poll, &$data, $u
 		break;
 
 		case 'reply':
-			$sql_data[TOPICS_TABLE]['stat'][] = 'topic_replies_real = topic_replies_real + 1, topic_bumped = 0, topic_bumper = 0' . (($post_approval) ? ', topic_replies = topic_replies + 1' : '') . ((!empty($data['attachment_data']) || (isset($data['topic_attachment']) && $data['topic_attachment'])) ? ', topic_attachment = 1' : '');
+			$sql_data[TOPICS_TABLE]['stat'][] = 'topic_last_view_time = ' . $current_time . ',
+				topic_replies_real = topic_replies_real + 1,
+				topic_bumped = 0,
+				topic_bumper = 0' .
+				(($post_approval) ? ', topic_replies = topic_replies + 1' : '') .
+				((!empty($data['attachment_data']) || (isset($data['topic_attachment']) && $data['topic_attachment'])) ? ', topic_attachment = 1' : '');
+
 			$sql_data[USERS_TABLE]['stat'][] = "user_lastpost_time = $current_time" . (($auth->acl_get('f_postcount', $data['forum_id']) && $post_approval) ? ', user_posts = user_posts + 1' : '');
 
 			if ($post_approval && $topic_type != POST_GLOBAL)
@@ -1824,6 +1831,7 @@ function submit_post($mode, $subject, $username, $topic_type, &$poll, &$data, $u
 				'poll_max_options'			=> (isset($poll['poll_options'])) ? $poll['poll_max_options'] : 1,
 				'poll_length'				=> (isset($poll['poll_options'])) ? $poll_length : 0,
 				'poll_vote_change'			=> (isset($poll['poll_vote_change'])) ? $poll['poll_vote_change'] : 0,
+				'topic_last_view_time'		=> $current_time,
 
 				'topic_attachment'			=> (!empty($data['attachment_data'])) ? 1 : (isset($data['topic_attachment']) ? $data['topic_attachment'] : 0),
 			);
@@ -1867,7 +1875,7 @@ function submit_post($mode, $subject, $username, $topic_type, &$poll, &$data, $u
 			// Correctly set back the topic replies and forum posts... but only if the post was approved before.
 			if (!$post_approval && $data['post_approved'])
 			{
-				$sql_data[TOPICS_TABLE]['stat'][] = 'topic_replies = topic_replies - 1';
+				$sql_data[TOPICS_TABLE]['stat'][] = 'topic_replies = topic_replies - 1, topic_last_view_time = ' . $current_time;
 				$sql_data[FORUMS_TABLE]['stat'][] = 'forum_posts = forum_posts - 1';
 
 				set_config_count('num_posts', -1, true);