diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index 33cbfc98a4..672589a64f 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -563,6 +563,11 @@ class Processor
 			return '';
 		}
 
+		if (in_array($activity['reply-to-id'], $activity['children'] ?? [])) {
+			Logger::notice('reply-to-id is already in the list of children', ['id' => $activity['reply-to-id'], 'children' => $activity['children'], 'depth' => count($activity['children'])]);
+			return '';
+		} 
+
 		self::addActivityId($activity['reply-to-id']);
 
 		$completion = $activity['completion-mode'] ?? Receiver::COMPLETION_NONE;
@@ -1632,6 +1637,11 @@ class Processor
 			return null;
 		}
 
+		if (!empty($child['children']) && in_array($url, $child['children'])) {
+			Logger::notice('id is already in the list of children', ['depth' => count($child['children']), 'children' => $child['children'], 'id' => $url]);
+			return null;
+		}
+
 		try {
 			$curlResult = HTTPSignature::fetchRaw($url, $uid);
 		} catch (\Exception $exception) {
@@ -1725,6 +1735,16 @@ class Processor
 		}
 
 		$ldactivity['recursion-depth'] = !empty($child['recursion-depth']) ? $child['recursion-depth'] + 1 : 0;
+		$ldactivity['children']        = $child['children'] ?? [];
+		// This check ist mostly superflous, since there are similar checks before. This covers the case, when the fetched id doesn't match the url
+		if (in_array($activity['id'], $ldactivity['children'])) {			
+			Logger::notice('Fetched id is already in the list of children. It will not be processed.', ['id' => $activity['id'], 'children' => $ldactivity['children'], 'depth' => count($ldactivity['children'])]);
+			return null;
+		}
+		if (!empty($child['id'])) {
+			$ldactivity['children'][] = $child['id'];
+		}
+
 
 		if ($object_actor != $actor) {
 			Contact::updateByUrlIfNeeded($object_actor);
@@ -1782,6 +1802,10 @@ class Processor
 				if (Processor::alreadyKnown($id, $child['id'] ?? '')) {
 					continue;
 				}
+				if (!empty($child['children']) && in_array($id, $child['children'])) {
+					Logger::debug('Replies id is already in the list of children', ['depth' => count($child['children']), 'children' => $child['children'], 'id' => $id]);
+					continue;
+				}
 				if (parse_url($id, PHP_URL_HOST) == parse_url($url, PHP_URL_HOST)) {
 					Logger::debug('Incluced activity will be processed', ['replies' => $url, 'id' => $id]);
 					self::processActivity($reply, $id, $child, '', Receiver::COMPLETION_REPLIES);
diff --git a/src/Protocol/ActivityPub/Queue.php b/src/Protocol/ActivityPub/Queue.php
index 53761585ff..b2e8cb301b 100644
--- a/src/Protocol/ActivityPub/Queue.php
+++ b/src/Protocol/ActivityPub/Queue.php
@@ -318,7 +318,7 @@ class Queue
 				self::retrial($id);
 				return false;
 			}
-			if (!Post::exists(['uri' => $entry['in-reply-to-id']])) {
+			if (!Processor::alreadyKnown($entry['in-reply-to-id'], '')) {
 				// This entry belongs to some other entry that need to be fetched first
 				if (Fetch::hasWorker($entry['in-reply-to-id'])) {
 					Logger::debug('Fetching of the activity is already queued', ['id' => $entry['activity-id'], 'reply-to-id' => $entry['in-reply-to-id']]);
@@ -327,6 +327,11 @@ class Queue
 				}
 				Fetch::add($entry['in-reply-to-id']);
 				$activity = json_decode($entry['activity'], true);
+				if (in_array($entry['in-reply-to-id'], $activity['children'] ?? [])) {
+					Logger::notice('reply-to-id is already in the list of children', ['id' => $entry['in-reply-to-id'], 'children' => $activity['children'], 'depth' => count($activity['children'])]);
+					self::retrial($id);
+					return false;
+				}
 				$activity['recursion-depth'] = 0;
 				$wid = Worker::add(Worker::PRIORITY_HIGH, 'FetchMissingActivity', $entry['in-reply-to-id'], $activity, '', Receiver::COMPLETION_ASYNC);
 				Fetch::setWorkerId($entry['in-reply-to-id'], $wid);
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index bab386979a..9660827cd3 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -757,6 +757,8 @@ class Receiver
 			$object_data['recursion-depth'] = $activity['recursion-depth'];
 		}
 
+		$object_data['children'] = $activity['children'] ?? [];
+
 		if (!self::routeActivities($object_data, $type, $push, true, $uid)) {
 			self::storeUnhandledActivity(true, $type, $object_data, $activity, $body, $uid, $trust_source, $push, $signer);
 			Queue::remove($object_data);