diff --git a/src/Formatters/IntegerFormatter.php b/src/Formatters/IntegerFormatter.php
index e424914..809e296 100644
--- a/src/Formatters/IntegerFormatter.php
+++ b/src/Formatters/IntegerFormatter.php
@@ -33,7 +33,7 @@ class IntegerFormatter implements IFormatter
             $digit = intval($arguments[1]);
         }
         $bn = Utils::toBn($value);
-        $bnHex = $bn->toHex();
+        $bnHex = $bn->toHex($bn->is_negative);
         $padded = mb_substr($bnHex, 0, 1);
 
         if ($padded !== 'f') {