diff --git a/php/OAuthSimple.php b/php/OAuthSimple.php
index 5212805..3c7749b 100644
--- a/php/OAuthSimple.php
+++ b/php/OAuthSimple.php
@@ -392,7 +392,7 @@ class OAuthSimple {
         $cLength = strlen($this->_nonce_chars);
         for ($i=0; $i < $length; $i++)
         {
-            $rnum = rand(0,$cLength);
+            $rnum = rand(0,$cLength - 1);
             $result .= substr($this->_nonce_chars,$rnum,1);
         }
         $this->_parameters['oauth_nonce'] = $result;