diff --git a/mod/wiki/renderer.php b/mod/wiki/renderer.php
index 31594b2..bf3d53e 100755
--- a/mod/wiki/renderer.php
+++ b/mod/wiki/renderer.php
@@ -390,6 +390,9 @@ class mod_wiki_renderer extends plugin_renderer_base {
                     }
                 } else {
                     $group = groups_get_group($subwiki->groupid);
+                    if (!$group) {
+                        return ;
+                    }
                     $users = groups_get_members($subwiki->groupid);
                     foreach ($users as $user) {
                         $options[$group->id][$group->name][$group->id . '-' . $user->id] = fullname($user);