diff --git a/src/Sha3.php b/src/Sha3.php
index 85d9bff..09e0d8c 100644
--- a/src/Sha3.php
+++ b/src/Sha3.php
@@ -262,7 +262,7 @@ private static function keccak32($in_raw, $capacity, $outputlength, $suffix, $ra
         $temp = str_pad($temp, $rsiz, "\x0", STR_PAD_RIGHT);
 
         $temp[$inlen] = chr($suffix);
-        $temp[$rsiz - 1] = chr($temp[$rsiz - 1] | 0x80);
+        $temp[$rsiz - 1] = chr(ord($temp[$rsiz - 1]) | 0x80);
 
         for ($i = 0; $i < $rsizw; $i++) {
             $t = unpack('v*', self::ourSubstr($temp, $i * 8, 8));