diff --git a/src/QUI/Memberships/Users/Handler.php b/src/QUI/Memberships/Users/Handler.php
index 11adb1ff6cb65da0b1ad448aa2dd239f26c98265..8a64b81f9673fcfb2453cdd52ca1eba6b34863d7 100644
--- a/src/QUI/Memberships/Users/Handler.php
+++ b/src/QUI/Memberships/Users/Handler.php
@@ -13,6 +13,8 @@
 use QUI\Memberships\Utils;
 use QUI\Permissions\Permission;
 
+use function is_string;
+
 class Handler extends Factory
 {
     /**
@@ -222,7 +224,7 @@ public function getIdsByMembershipId(int $membershipId, bool $includeArchived =
      */
     public function getMembershipUsersByUserId(int | string $userId, bool $includeArchived = false): array
     {
-        if (is_int($userId)) {
+        if (is_string($userId)) {
             try {
                 $userId = QUI::getUsers()->get($userId)->getId();
             } catch (QUI\Exception) {