diff --git a/src/Manticore.php b/src/Manticore.php
index e12de1a..fcf8059 100644
--- a/src/Manticore.php
+++ b/src/Manticore.php
@@ -230,7 +230,7 @@ class Manticore
         );
     }
 
-    private function _crc32(mixed $value): int
+    private function _crc32(string $value): int
     {
         return crc32(
             $value