diff --git a/src/OAuth2/Util/SecureKey.php b/src/OAuth2/Util/SecureKey.php
index 0739a193..eaa741c7 100644
--- a/src/OAuth2/Util/SecureKey.php
+++ b/src/OAuth2/Util/SecureKey.php
@@ -16,6 +16,6 @@ class SecureKey
             throw new Exception('Error Generating Key');
         }
 
-        return substr(str_replace(['/', '+', '='], '', base64_encode($bytes)), 0, $len);
+        return substr(str_replace(array('/', '+', '='), '', base64_encode($bytes)), 0, $len);
     }
 }
\ No newline at end of file