diff --git a/mod/glossary/print.php b/mod/glossary/print.php
index 842148117bf..d0d08aa1bf0 100644
--- a/mod/glossary/print.php
+++ b/mod/glossary/print.php
@@ -11,7 +11,7 @@ $offset        = optional_param('offset', 0, PARAM_INT);              // number
 $displayformat = optional_param('displayformat',-1, PARAM_INT);
 
 $mode    = required_param('mode', PARAM_ALPHA);             // mode to show the entries
-$hook    = optional_param('hook','ALL', PARAM_ALPHANUM);   // what to show
+$hook    = optional_param('hook','ALL', PARAM_CLEAN);       // what to show
 $sortkey = optional_param('sortkey','UPDATE', PARAM_ALPHA); // Sorting key
 
 $url = new moodle_url('/mod/glossary/print.php', array('id'=>$id));