diff --git a/phpseclib/Crypt/Base.php b/phpseclib/Crypt/Base.php
index 1336d0ef..e88476b9 100644
--- a/phpseclib/Crypt/Base.php
+++ b/phpseclib/Crypt/Base.php
@@ -537,13 +537,13 @@ class Crypt_Base
         if (!defined('CRYPT_BASE_USE_REG_INTVAL')) {
             switch (true) {
                 // PHP 5.3, per http://php.net/releases/5_3_0.php, introduced "more consistent float rounding"
-                case version_compare(PHP_VERSION, '5.3.0') >= 0 && (php_uname('m') & "\xDF\xDF\xDF") != 'ARM':
+                case version_compare(PHP_VERSION, '5.3.0') >= 0 && !(is_string(php_uname('m')) && (php_uname('m') & "\xDF\xDF\xDF") == 'ARM'):
                 // PHP_OS & "\xDF\xDF\xDF" == strtoupper(substr(PHP_OS, 0, 3)), but a lot faster
                 case (PHP_OS & "\xDF\xDF\xDF") === 'WIN':
                 case PHP_INT_SIZE == 8:
                     define('CRYPT_BASE_USE_REG_INTVAL', true);
                     break;
-                case (php_uname('m') & "\xDF\xDF\xDF") == 'ARM':
+                case is_string(php_uname('m')) && (php_uname('m') & "\xDF\xDF\xDF") == 'ARM':
                     switch (true) {
                         // PHP_VERSION_ID wasn't a constant until PHP 5.2.7
                         case version_compare(PHP_VERSION, '5.3.0') < 1: