diff --git a/phpBB/includes/mcp/mcp_topic.php b/phpBB/includes/mcp/mcp_topic.php
index 7d4edaf362..36cfe1e355 100644
--- a/phpBB/includes/mcp/mcp_topic.php
+++ b/phpBB/includes/mcp/mcp_topic.php
@@ -626,6 +626,14 @@ function merge_posts($topic_id, $to_topic_id)
 			$db->sql_return_on_error(false);
 
 			$db->sql_query('DELETE FROM ' . TOPICS_WATCH_TABLE . ' WHERE topic_id = ' . (int) $topic_id);
+
+			// If the topic no longer exist, we will update the bookmarks table.
+			// To not let it error out on users who bookmarked both topics, we just return on an error...
+			$db->sql_return_on_error(true);
+			$db->sql_query('UPDATE ' . BOOKMARKS_TABLE . ' SET topic_id = ' . (int) $to_topic_id . ' WHERE topic_id = ' . (int) $topic_id);
+			$db->sql_return_on_error(false);
+
+			$db->sql_query('DELETE FROM ' . BOOKMARKS_TABLE . ' WHERE topic_id = ' . (int) $topic_id);
 		}
 
 		// Link to the new topic
@@ -650,4 +658,4 @@ function merge_posts($topic_id, $to_topic_id)
 	}
 }
 
-?>
\ No newline at end of file
+?>