diff --git a/src/externalldap.js b/src/externalldap.js
index dbc0cb162..0eead2dc3 100644
--- a/src/externalldap.js
+++ b/src/externalldap.js
@@ -204,7 +204,7 @@ function sync(progressCallback, callback) {
                             } else if (result.email !== user.mail || result.displayName !== user.cn) {
                                 debug('[updating user]', user.uid, user.mail, user.cn);
 
-                                users.update(result.id, { email: user.mail, displayName: user.cn }, auditsource.EXTERNAL_LDAP_TASK, function (error) {
+                                users.update(result.id, { email: user.mail, fallbackEmail: user.mail, displayName: user.cn }, auditsource.EXTERNAL_LDAP_TASK, function (error) {
                                     if (error) console.error('Failed to update user', user, error);
                                     callback();
                                 });