diff --git a/app/code/community/Amazon/Payments/Model/System/Config/Backend/Popupcomment.php b/app/code/community/Amazon/Payments/Model/System/Config/Backend/Popupcomment.php
index 880b216..a054d13 100644
--- a/app/code/community/Amazon/Payments/Model/System/Config/Backend/Popupcomment.php
+++ b/app/code/community/Amazon/Payments/Model/System/Config/Backend/Popupcomment.php
@@ -19,7 +19,7 @@ public function getCommentText(Mage_Core_Model_Config_Element $element, $current
 
         $replace_cleanup = array(':80', ':443');
 
-        if (in_array('mod_rewrite', apache_get_modules())) {
+        if (function_exists('apache_get_modules') && in_array('mod_rewrite', apache_get_modules())) {
             $replace_cleanup[] = 'index.php/';
         }