diff --git a/apps/user_ldap/lib/Group_LDAP.php b/apps/user_ldap/lib/Group_LDAP.php
index 5444f0815e..e396999f86 100644
--- a/apps/user_ldap/lib/Group_LDAP.php
+++ b/apps/user_ldap/lib/Group_LDAP.php
@@ -170,9 +170,14 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 				if (count($filterParts) > 0) {
 					$filter = $this->access->combineFilterWithOr($filterParts);
 					$users = $this->access->fetchListOfUsers($filter, $requestAttributes, count($filterParts));
-					$dns = array_merge($dns, $users);
+					$dns = array_reduce($users, function (array $carry, array $record) {
+						if (!in_array($carry, $record['dn'][0])) {
+							$carry[$record['dn'][0]] = 1;
+						}
+						return $carry;
+					}, $dns);
 				}
-				$members = $dns;
+				$members = array_keys($dns);
 				break;
 		}