diff --git a/include/conversation.php b/include/conversation.php
index b163184af9..1f597756f4 100644
--- a/include/conversation.php
+++ b/include/conversation.php
@@ -799,7 +799,7 @@ function conversation_add_children(array $parents, $block_authors, $order, $uid)
  */
 function conversation_fetch_items(array $parent, array $items, array $condition, bool $block_authors, array $params) {
 	if ($block_authors) {
-		$condition[0] .= "AND NOT `author`.`hidden`";
+		$condition[0] .= " AND NOT `author`.`hidden`";
 	}
 
 	$thread_items = Item::selectForUser(local_user(), array_merge(Item::DISPLAY_FIELDLIST, ['contact-uid', 'gravity']), $condition, $params);