--- a/inc/api/request.php
+++ b/inc/api/request.php
@@ -101,6 +101,7 @@ class api_request {
             /* if you set an extension: [xml, foo, rss, html] node in your
              * config file, only these extensions are valid extensions.
              * the rest is not parsed as an extension */
+            if (isset($extensions['allowed'])) {
             $aExtensions = $extensions['allowed'];

             if (preg_match("#\.([a-z]+)$#", $this->filename, $matches)) {
@@ -109,6 +110,7 @@ class api_request {
                 }
             }
         }
+        }
         if (!$this->extension) {
             $this->extension = isset($extensions['default']) ? $extensions['default'] : 'html';
         }