diff --git a/src/Binary.php b/src/Binary.php
index 0643fb9f641bc0facc555d9b1dcb0cad99fd631c..add0522896ce1b39f14fbdea8868f7e1f43f1c13 100644
--- a/src/Binary.php
+++ b/src/Binary.php
@@ -69,7 +69,7 @@ abstract class Binary
     public static function safeSubstr(
         string $str,
         int $start = 0,
-        int $length = null
+        $length = null
     ): string {
         if ($length === 0) {
             return '';