diff --git a/src/Validation/EsValidation.php b/src/Validation/EsValidation.php
index 015e2a0..8dd69af 100644
--- a/src/Validation/EsValidation.php
+++ b/src/Validation/EsValidation.php
@@ -114,7 +114,7 @@ public static function nie(string $check): bool
 
         array_shift($matches);
         [$first, $num, $letter] = $matches;
-        $num = strtr($first, 'XYZ', '012') . $num;
+        $num = (int)(strtr($first, 'XYZ', '012') . $num);
 
         return $letter === static::$CODES[$num % 23];
     }