diff --git a/lib/Controller/RoomController.php b/lib/Controller/RoomController.php
index 43fbd040d..53c95f17c 100644
--- a/lib/Controller/RoomController.php
+++ b/lib/Controller/RoomController.php
@@ -498,7 +498,13 @@ class RoomController extends AEnvironmentAwareController {
 				$lastReadMessage = $this->chatManager->getLastReadMessageFromLegacy($room, $currentUser);
 				$currentParticipant->setLastReadMessage($lastReadMessage);
 			}
-			$roomData['unreadMessages'] = $this->chatManager->getUnreadCount($room, $lastReadMessage);
+			if ($room->getLastMessage() && $lastReadMessage === (int) $room->getLastMessage()->getId()) {
+				// When the last message is the last read message, there are no unread messages,
+				// so we can save the query.
+				$roomData['unreadMessages'] = 0;
+			} else {
+				$roomData['unreadMessages'] = $this->chatManager->getUnreadCount($room, $lastReadMessage);
+			}
 
 			$lastMention = $currentParticipant->getLastMentionMessage();
 			$roomData['unreadMention'] = $lastMention !== 0 && $lastReadMessage < $lastMention;