diff --git a/lib/Chat/Notifier.php b/lib/Chat/Notifier.php
index 310d9c42325..f7aa5c592ee 100644
--- a/lib/Chat/Notifier.php
+++ b/lib/Chat/Notifier.php
@@ -270,7 +270,13 @@ public function notifyReacted(Room $chat, IComment $comment, IComment $reaction)
 			return;
 		}
 
-		$participant = $chat->getParticipant($comment->getActorId(), false);
+
+		try {
+			$participant = $chat->getParticipant($comment->getActorId(), false);
+		} catch (ParticipantNotFoundException $e) {
+			return;
+		}
+
 		$notificationLevel = $participant->getAttendee()->getNotificationLevel();
 		if ($notificationLevel === Participant::NOTIFY_DEFAULT) {
 			if ($chat->getType() === Room::TYPE_ONE_TO_ONE) {
diff --git a/tests/integration/features/reaction/react.feature b/tests/integration/features/reaction/react.feature
index 85cc1007c4f..1ddd933bfe6 100644
--- a/tests/integration/features/reaction/react.feature
+++ b/tests/integration/features/reaction/react.feature
@@ -60,6 +60,23 @@ Feature: reaction/react
       | room | users     | participant1 | participant1-displayname | user_added |
       | room | users     | participant1 | participant1-displayname | conversation_created |
 
+  Scenario: React to message does not fail when the author left the conversation
+    Given user "participant1" creates room "room" (v4)
+      | roomType | 3 |
+      | roomName | room |
+    And user "participant1" adds user "participant2" to room "room" with 200 (v4)
+    And user "participant2" sends message "Message 1" to room "room" with 201
+    And user "participant2" removes themselves from room "room" with 200 (v4)
+    And user "participant1" react with "👍" on message "Message 1" to room "room" with 201
+      | actorType | actorId      | actorDisplayName         | reaction |
+      | users     | participant1 | participant1-displayname | 👍       |
+    Then user "participant1" sees the following system messages in room "room" with 200
+      | room | actorType | actorId      | actorDisplayName         | systemMessage |
+      | room | users     | participant1 | participant1-displayname | reaction |
+      | room | users     | participant2 | participant2-displayname | user_removed |
+      | room | users     | participant1 | participant1-displayname | user_added |
+      | room | users     | participant1 | participant1-displayname | conversation_created |
+
   Scenario: Delete reaction to message with success
     Given user "participant1" creates room "room" (v4)
       | roomType | 3 |