diff --git a/src/Helpers/Validate.php b/src/Helpers/Validate.php
index a9593dd..f782a14 100644
--- a/src/Helpers/Validate.php
+++ b/src/Helpers/Validate.php
@@ -130,7 +130,7 @@ public static function isValidCns($cns)
 
         $first = (int) $cns[0];
 
-        if (in_array($first, [7, 8, 9])) {
+        if (in_array($first, [5, 7, 8, 9])) {
             return Validate::validate_cns_tmp($cns);
         }
 
diff --git a/tests/Helpers/ValidateTest.php b/tests/Helpers/ValidateTest.php
index 310b5eb..9abd100 100644
--- a/tests/Helpers/ValidateTest.php
+++ b/tests/Helpers/ValidateTest.php
@@ -161,6 +161,11 @@ public function cnsProvider()
             ['796 3683 5437 0018', true],
             ['796 3683 54370018', true],
             ['7963683 54370018', true],
+            ['550354737380003', true],
+            ['521473152170018', true],
+            ['503521996570006', false],
+            ['556492895730003', false],
+            ['584480646290007', false],
             ['696368354370018', false],
             ['7963683543700120', false],
             ['', false],