diff --git a/src/enums/MDInstitutionExternalIdRepository.php b/src/enums/MDInstitutionExternalIdRepository.php
index c00b442..fc7a36d 100644
--- a/src/enums/MDInstitutionExternalIdRepository.php
+++ b/src/enums/MDInstitutionExternalIdRepository.php
@@ -19,7 +19,7 @@ enum MDInstitutionExternalIdRepository implements MDValueEnumInterface, JsonSeri
     ];
 
     const VALIDATION_PATTERN_PHP = [
-        'hu_ksh' => '[0-9]{8}-[0-9]{4}-[0-9]{3}-[0-9]{2}',
+        'hu_ksh' => '/^[0-9]{8}-[0-9]{4}-[0-9]{3}-[0-9]{2}$/',
     ];
 
     /**