diff --git a/mod/lockview.php b/mod/lockview.php
index af57730c8a..9f9dcfea42 100644
--- a/mod/lockview.php
+++ b/mod/lockview.php
@@ -64,10 +64,10 @@ function lockview_content(App $a)
 	/** @var ACLFormatter $aclFormatter */
 	$aclFormatter = BaseObject::getClass(ACLFormatter::class);
 
-	$allowed_users = $aclFormatter->expand($item['allow_cid'] ?? '');
-	$allowed_groups = $aclFormatter->expand($item['allow_gid'] ?? '');
-	$deny_users = $aclFormatter->expand($item['deny_cid'] ?? '');
-	$deny_groups = $aclFormatter->expand($item['deny_gid'] ?? '');
+	$allowed_users = $aclFormatter->expand($item['allow_cid']);
+	$allowed_groups = $aclFormatter->expand($item['allow_gid']);
+	$deny_users = $aclFormatter->expand($item['deny_cid']);
+	$deny_groups = $aclFormatter->expand($item['deny_gid']);
 
 	$o = L10n::t('Visible to:') . '<br />';
 	$l = [];
diff --git a/src/Model/Item.php b/src/Model/Item.php
index e298cc1605..9501c8e5d2 100644
--- a/src/Model/Item.php
+++ b/src/Model/Item.php
@@ -2904,10 +2904,10 @@ class Item extends BaseObject
 		/** @var ACLFormatter $aclFormater */
 		$aclFormater = self::getClass(ACLFormatter::class);
 
-		$allow_people = $aclFormater->expand($obj['allow_cid'] ?? '');
-		$allow_groups = Group::expand($obj['uid'], $aclFormater->expand($obj['allow_gid'] ?? ''), $check_dead);
-		$deny_people  = $aclFormater->expand($obj['deny_cid'] ?? '');
-		$deny_groups  = Group::expand($obj['uid'], $aclFormater->expand($obj['deny_gid'] ?? ''), $check_dead);
+		$allow_people = $aclFormater->expand($obj['allow_cid']);
+		$allow_groups = Group::expand($obj['uid'], $aclFormater->expand($obj['allow_gid']), $check_dead);
+		$deny_people  = $aclFormater->expand($obj['deny_cid']);
+		$deny_groups  = Group::expand($obj['uid'], $aclFormater->expand($obj['deny_gid']), $check_dead);
 		$recipients   = array_unique(array_merge($allow_people, $allow_groups));
 		$deny         = array_unique(array_merge($deny_people, $deny_groups));
 		$recipients   = array_diff($recipients, $deny);
diff --git a/src/Module/Item/Compose.php b/src/Module/Item/Compose.php
index 0d3b4eaac2..c44e4c61ab 100644
--- a/src/Module/Item/Compose.php
+++ b/src/Module/Item/Compose.php
@@ -74,8 +74,8 @@ class Compose extends BaseModule
 				$compose_title = L10n::t('Compose new post');
 				$type = 'post';
 				$doesFederate = true;
-				$contact_allow = implode(',', $aclFormatter->expand($user['allow_cid'] ?? ''));
-				$group_allow = implode(',', $aclFormatter->expand($user['allow_gid'] ?? '')) ?: Group::FOLLOWERS;
+				$contact_allow = implode(',', $aclFormatter->expand($user['allow_cid']));
+				$group_allow = implode(',', $aclFormatter->expand($user['allow_gid'])) ?: Group::FOLLOWERS;
 				break;
 		}
 
@@ -86,8 +86,8 @@ class Compose extends BaseModule
 		$wall          = $_REQUEST['wall']          ?? $type == 'post';
 		$contact_allow = $_REQUEST['contact_allow'] ?? $contact_allow;
 		$group_allow   = $_REQUEST['group_allow']   ?? $group_allow;
-		$contact_deny  = $_REQUEST['contact_deny']  ?? implode(',', $aclFormatter->expand($user['deny_cid'] ?? ''));
-		$group_deny    = $_REQUEST['group_deny']    ?? implode(',', $aclFormatter->expand($user['deny_gid'] ?? ''));
+		$contact_deny  = $_REQUEST['contact_deny']  ?? implode(',', $aclFormatter->expand($user['deny_cid']));
+		$group_deny    = $_REQUEST['group_deny']    ?? implode(',', $aclFormatter->expand($user['deny_gid']));
 		$visibility    = ($contact_allow . $user['allow_gid'] . $user['deny_cid'] . $user['deny_gid']) ? 'custom' : 'public';
 
 		$acl_contacts = Contact::selectToArray(['id', 'name', 'addr', 'micro'], ['uid' => local_user(), 'pending' => false, 'rel' => [Contact::FOLLOWER, Contact::FRIEND]]);
diff --git a/src/Util/ACLFormatter.php b/src/Util/ACLFormatter.php
index 4a36f3ebf2..d194e2e67e 100644
--- a/src/Util/ACLFormatter.php
+++ b/src/Util/ACLFormatter.php
@@ -12,12 +12,17 @@ final class ACLFormatter
 	/**
 	 * Turn user/group ACLs stored as angle bracketed text into arrays
 	 *
-	 * @param string $ids A angle-bracketed list of IDs
+	 * @param string|null $ids A angle-bracketed list of IDs
 	 *
-	 * @return array The array based on the IDs
+	 * @return array|null The array based on the IDs (null in case there is no list)
 	 */
-	public function expand(string $ids)
+	public function expand(string $ids = null)
 	{
+		// In case there is no ID list, return null (=> no ACL set)
+		if (!isset($ids)) {
+			return null;
+		}
+
 		// turn string array of angle-bracketed elements into numeric array
 		// e.g. "<1><2><3>" => array(1,2,3);
 		preg_match_all('/<(' . Group::FOLLOWERS . '|'. Group::MUTUALS . '|[0-9]+)>/', $ids, $matches, PREG_PATTERN_ORDER);
@@ -31,12 +36,18 @@ final class ACLFormatter
 	 * @param string $item The item to sanitise
 	 */
 	private function sanitize(string &$item) {
+		// The item is an ACL int value
 		if (intval($item)) {
 			$item = '<' . intval(Strings::escapeTags(trim($item))) . '>';
+		// The item is a allowed ACL character
 		} elseif (in_array($item, [Group::FOLLOWERS, Group::MUTUALS])) {
 			$item = '<' . $item . '>';
-		} else {
+		// The item is already a ACL string
+		} elseif (preg_match('/<\d+?>/', $item)) {
 			unset($item);
+		// The item is not supported, so remove it (cleanup)
+		} else {
+			$item = '';
 		}
 	}
 
diff --git a/src/Worker/Notifier.php b/src/Worker/Notifier.php
index 9ab07e6d49..8b6be76b50 100644
--- a/src/Worker/Notifier.php
+++ b/src/Worker/Notifier.php
@@ -279,10 +279,10 @@ class Notifier
 				/** @var ACLFormatter $aclFormatter */
 				$aclFormatter = BaseObject::getClass(ACLFormatter::class);
 
-				$allow_people = $aclFormatter->expand($parent['allow_cid'] ?? '');
-				$allow_groups = Group::expand($uid, $aclFormatter->expand($parent['allow_gid'] ?? ''),true);
-				$deny_people  = $aclFormatter->expand($parent['deny_cid'] ?? '');
-				$deny_groups  = Group::expand($uid, $aclFormatter->expand($parent['deny_gid'] ?? ''));
+				$allow_people = $aclFormatter->expand($parent['allow_cid']);
+				$allow_groups = Group::expand($uid, $aclFormatter->expand($parent['allow_gid']),true);
+				$deny_people  = $aclFormatter->expand($parent['deny_cid']);
+				$deny_groups  = Group::expand($uid, $aclFormatter->expand($parent['deny_gid']));
 
 				// if our parent is a public forum (forum_mode == 1), uplink to the origional author causing
 				// a delivery fork. private groups (forum_mode == 2) do not uplink
diff --git a/tests/src/Util/ACLFormaterTest.php b/tests/src/Util/ACLFormaterTest.php
index ac5b25e6c2..630a30e40b 100644
--- a/tests/src/Util/ACLFormaterTest.php
+++ b/tests/src/Util/ACLFormaterTest.php
@@ -164,15 +164,14 @@ class ACLFormaterTest extends TestCase
 	}
 
 	/**
-	 * Test expected exception in case of wrong typehint
-	 *
-	 * @expectedException Error
+	 * Test nullable expand (=> no ACL set)
 	 */
 	public function testExpandNull()
 	{
 		$aclFormatter = new ACLFormatter();
 
-		$aclFormatter->expand(null);
+		$this->assertNull($aclFormatter->expand(null));
+		$this->assertNull($aclFormatter->expand());
 	}
 
 	public function dataAclToString()
@@ -198,6 +197,23 @@ class ACLFormaterTest extends TestCase
 				'input'  => 'a,bsd23,4',
 				'assert' => '<4>',
 			],
+			/** @see https://github.com/friendica/friendica/pull/7787 */
+			'bug-7778-angle-brackets' => [
+				'input' => ["<40195>"],
+				'assert' => "<40195>",
+			],
+			Group::FOLLOWERS => [
+				'input' => [Group::FOLLOWERS, 1],
+				'assert' => '<' . Group::FOLLOWERS . '><1>',
+			],
+			Group::MUTUALS => [
+				'input' => [Group::MUTUALS, 1],
+				'assert' => '<' . Group::MUTUALS . '><1>',
+			],
+			'wrong-angle-brackets' => [
+				'input' => ["<asd>","<123>"],
+				'assert' => "<123>",
+			],
 		];
 	}