diff --git a/src/Model/Notification.php b/src/Model/Notification.php
index 03bfafe782..b0294aa8a4 100644
--- a/src/Model/Notification.php
+++ b/src/Model/Notification.php
@@ -193,7 +193,7 @@ class Notification extends BaseModel
 		$announce = Verb::getID(Activity::ANNOUNCE);
 		$post     = Verb::getID(Activity::POST);
 
-		if (in_array($notification['type'], [Post\UserNotification::NOTIF_THREAD_COMMENT, Post\UserNotification::NOTIF_COMMENT_PARTICIPATION, Post\UserNotification::NOTIF_EXPLICIT_TAGGED])) {
+		if (in_array($notification['type'], [Post\UserNotification::NOTIF_THREAD_COMMENT, Post\UserNotification::NOTIF_COMMENT_PARTICIPATION, Post\UserNotification::NOTIF_ACTIVITY_PARTICIPATION, Post\UserNotification::NOTIF_EXPLICIT_TAGGED])) {
 			$item = Post::selectFirst([], ['uri-id' => $notification['parent-uri-id'], 'uid' => [0, $notification['uid']]], ['order' => ['uid' => true]]);
 			if (empty($item)) {
 				Logger::info('Parent post not found', ['uri-id' => $notification['parent-uri-id']]);
@@ -221,6 +221,12 @@ class Notification extends BaseModel
 				Logger::info('Causer not found', ['causer' => $item['causer-id']]);
 				return $message;
 			}
+		} elseif (in_array($notification['type'], [Post\UserNotification::NOTIF_COMMENT_PARTICIPATION, Post\UserNotification::NOTIF_ACTIVITY_PARTICIPATION])) {
+			$contact = Contact::getById($item['author-id'], ['id', 'name', 'url']);
+			if (empty($contact)) {
+				Logger::info('Author not found', ['author' => $item['author-id']]);
+				return $message;
+			}
 		}
 
 		$link = DI::baseUrl() . '/display/' . urlencode($item['guid']);
@@ -284,11 +290,16 @@ class Notification extends BaseModel
 						break;
 
 					case Post\UserNotification::NOTIF_COMMENT_PARTICIPATION:
-						$msg = $l10n->t('%1$s commented in the thread %2$s');
-						break;
-
 					case Post\UserNotification::NOTIF_ACTIVITY_PARTICIPATION:
-						// Unhandled
+						if (($causer['id'] == $contact['id']) && ($title != '')) {
+							$msg = $l10n->t('%1$s commented in their thread %2$s');
+						} elseif ($causer['id'] == $contact['id']) {
+							$msg = $l10n->t('%1$s commented in their thread');
+						} elseif ($title != '') {
+							$msg = $l10n->t('%1$s commented in the thread %2$s from %3$s');
+						} else {
+							$msg = $l10n->t('%1$s commented in the thread from %3$s');
+						}
 						break;
 
 					case Post\UserNotification::NOTIF_DIRECT_THREAD_COMMENT:
diff --git a/view/lang/C/messages.po b/view/lang/C/messages.po
index d5207ba9e1..203680c3d9 100644
--- a/view/lang/C/messages.po
+++ b/view/lang/C/messages.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: 2021.09-dev\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2021-08-21 20:27+0000\n"
+"POT-Creation-Date: 2021-08-22 03:57+0000\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1774,15 +1774,15 @@ msgstr ""
 msgid "View Album"
 msgstr ""
 
-#: mod/ping.php:286
+#: mod/ping.php:287
 msgid "{0} wants to be your friend"
 msgstr ""
 
-#: mod/ping.php:303
+#: mod/ping.php:304
 msgid "{0} requested registration"
 msgstr ""
 
-#: mod/ping.php:316
+#: mod/ping.php:317
 #, php-format
 msgid "{0} and %d others requested registration"
 msgstr ""
@@ -4665,82 +4665,97 @@ msgstr ""
 msgid "[no subject]"
 msgstr ""
 
-#: src/Model/Notification.php:241
+#: src/Model/Notification.php:247
 #, php-format
 msgid "%1$s liked your comment %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:244
+#: src/Model/Notification.php:250
 #, php-format
 msgid "%1$s liked your post %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:251
+#: src/Model/Notification.php:257
 #, php-format
 msgid "%1$s disliked your comment %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:254
+#: src/Model/Notification.php:260
 #, php-format
 msgid "%1$s disliked your post %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:261
+#: src/Model/Notification.php:267
 #, php-format
 msgid "%1$s shared your comment %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:264
+#: src/Model/Notification.php:270
 #, php-format
 msgid "%1$s shared your post %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:271
+#: src/Model/Notification.php:277
 #, php-format
 msgid "%1$s tagged you on %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:275
+#: src/Model/Notification.php:281
 #, php-format
 msgid "%1$s replied to you on %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:279
+#: src/Model/Notification.php:285
 #, php-format
 msgid "%1$s commented in your thread %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:283
+#: src/Model/Notification.php:289
 #, php-format
 msgid "%1$s commented on your comment %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:287
+#: src/Model/Notification.php:295
 #, php-format
-msgid "%1$s commented in the thread %2$s"
+msgid "%1$s commented in their thread %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:295
+#: src/Model/Notification.php:297
+#, php-format
+msgid "%1$s commented in their thread"
+msgstr ""
+
+#: src/Model/Notification.php:299
+#, php-format
+msgid "%1$s commented in the thread %2$s from %3$s"
+msgstr ""
+
+#: src/Model/Notification.php:301
+#, php-format
+msgid "%1$s commented in the thread from %3$s"
+msgstr ""
+
+#: src/Model/Notification.php:306
 #, php-format
 msgid "%1$s commented on your thread %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:300
+#: src/Model/Notification.php:311
 #, php-format
 msgid "%1$s shared the post %2$s from %3$s"
 msgstr ""
 
-#: src/Model/Notification.php:302
+#: src/Model/Notification.php:313
 #, php-format
 msgid "%1$s shared a post from %3$s"
 msgstr ""
 
-#: src/Model/Notification.php:304
+#: src/Model/Notification.php:315
 #, php-format
 msgid "%1$s shared the post %2$s"
 msgstr ""
 
-#: src/Model/Notification.php:306
+#: src/Model/Notification.php:317
 #, php-format
 msgid "%1$s shared a post"
 msgstr ""