diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 52ae892d..3524668e 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -137,8 +137,8 @@ class BigInteger implements \JsonSerializable
         if (!isset(self::$mainEngine)) {
             $engines = [
                 ['GMP'],
-                ['BCMath', ['OpenSSL']],
                 ['PHP64', ['OpenSSL']],
+                ['BCMath', ['OpenSSL']],
                 ['PHP32', ['OpenSSL']],
                 ['PHP64', ['DefaultEngine']],
                 ['PHP32', ['DefaultEngine']]