diff --git a/actions/foaf.php b/actions/foaf.php
index 9cb65a8856..2f054de0c9 100644
--- a/actions/foaf.php
+++ b/actions/foaf.php
@@ -95,7 +95,9 @@ class FoafAction extends Action
         // Would be nice to tell if they were a Person or not (e.g. a #person usertag?)
         $this->elementStart('Agent', array('rdf:about' =>
                                              $this->user->uri));
-        $this->element('mbox_sha1sum', null, sha1('mailto:' . $this->user->email));
+        if ($this->user->email) {
+            $this->element('mbox_sha1sum', null, sha1('mailto:' . $this->user->email));
+        }
         if ($this->profile->fullname) {
             $this->element('name', null, $this->profile->fullname);
         }