diff --git a/src/Client.php b/src/Client.php
index 55bbfd6..6fb7ecc 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -194,7 +194,7 @@ public function upload(array $options)
         } else {
             // We've been given a simple string body, it's super simple to calculate the hash and size.
             $hash = sha1($options['Body']);
-            $size = mb_strlen($options['Body']);
+            $size = strlen($options['Body']);
         }
 
         if (!isset($options['FileLastModified'])) {